Download Fonctionnement de la Messagerie Electronique or Email

2007
Initiation
à l’Informatique
Classe de Seconde, Retho et Philo
Technicien en Electronique
Version Anglaise
Prepared by:
Enseigner et Apprendre avec la Technologie
Il est important de comprendre qu’un ordinateur n’est pas
seulement un outil de travail permettant aux utilisateurs d’échanger
des email ou de préparer électroniquement leurs devoirs en
accédant rapidement aux informations utiles et même très rares
dans le passé, ou, un moyen sûr et rapide audio visuel de
communiquer entre familles et amis. On dirait de préférence
qu’une meilleure connaissance d’utilisation d’un système informatique est vraiment utile, nécessaire et
indispensable à tous pour pouvoir maîtriser ses avantages en profitant de savourer le système de la
globalisation pour une participation active dans tous les niveaux. Une bonne connaissance de son
utilisation est une obligation, plus vous le maîtrisez, mieux vous comprenez son rôle au développement.
L'ÉDUCATION ET LA NOUVELLE TECHNOLOGIE POUR LE 21ème SIÈCLE
(Internationale de l'Education - novembre 1995)
Nous proposons ici quelques extraits du texte sur les Nouvelles Technologies adopté, en complément du
rapport général, par la Conférence de Madrid (novembre 1995) de l'Internationale de l'Education (IE).
Ce texte nous a été adressé par le SNES dont le Secrétaire Général adjoint, Louis Weber, a été récemment
élu Vice-président du Comité européen de l'IE, regroupant la grande majorité des syndicats enseignants
d'Europe. Nous tenons l'intégralité de ce texte (15 pages) à la disposition des adhérents intéressés, contre 5
timbres à 3,00 F pour frais de photocopie et d'envoi.
1. PRIORITÉS DE L'IE/EUROPE
« Il existe une tendance à surestimer les difficultés quant à l'usage de la nouvelle technologie, et à la
présenter comme quelque chose d'ésotérique. Il est important que les ordinateurs et les autres aides
électroniques soient intégrés dans la pratique quotidienne de l'éducation sous toutes ses formes, du
préscolaire au postsecondaire, tout comme ils le sont dans divers secteurs de la société...
Les écoles, de quelque type qu'elles soient, ont notamment pour tâche de préparer les enfants et les jeunes à
la vie adulte ; c'est pourquoi, s'agissant de la technologie comme d'autres aspects, elles doivent tendre à
l'universalité de l'éducation, dans laquelle les enfants et les jeunes, où qu'ils vivent, quelle que soit la
richesse de leurs parents ou autres facteurs du même ordre, auront accès à des outils de travail modernes au
cours de leur développement...
Les gouvernements nationaux et locaux doivent prendre pleinement leurs responsabilités, tout comme
d'ailleurs les directions des écoles et les enseignants... ».
2. LES ENSEIGNANTS DOIVENT PRENDRE LA TÊTE DU DÉVELOPPEMENT DU SAVOIR
« L'introduction de la technologie de l'information dans la société impose à présent des exigences
entièrement nouvelles aux enseignants et à leurs organisations. Les enseignants, en tant que groupe
professionnel, ne doivent pas seulement rester à la hauteur des développements de la technologie de
l'information et être en mesure d'y participer tant sur le plan constructif que sur le plan critique, mais ils
doivent également prendre la tête du développement du savoir dans tous les domaines du secteur de
l'éducation, et à certains points de vue, dans des conditions entièrement nouvelles...
Le rôle de l'enseignant subira des transformations successives. Dans de nombreux domaines, l'enseignant
deviendra davantage un guide qu'un pourvoyeur de savoir au sens traditionnel du terme. Pour réussir dans
cette démarche, l'enseignant doit se trouver lui-même dans une disposition d'esprit orientée vers l'activité et
la recherche. En outre, l'enseignant engagé dans un processus de formation continue est toujours le meilleur
enseignant...
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Le choix des méthodes de travail doit être régi par les objectifs éducatifs. Le développement de ces
méthodes nécessite une vision claire et un engagement de la part de la direction de l'école, qui doit
également être en mesure de transposer ces perspectives dans une action pratiques...
Il doit être absolument exclu que des entreprises informatiques régissent le développement de la
technologie de l'information dans le secteur de l'éducation par le biais de leurs concepteurs...
Le type d'ordinateur et de logiciel choisi pour un programme d'études déterminé devrait être arrêté après
des discussions à l'échelon local. La chose importante est que le besoin de disposer de la nouvelle
technologie ainsi que son développement devraient toujours être inclus dans les délibérations relatives au
plan éducatif, tant à l'échelon général (c'est-à-dire pour l'école entière) qu'à un degré de détail plus poussé
(c'est-à-dire dans les discussions sur les matières ou les domaines d'études spécifiques)...».
3. EXIGENCES FONDAMENTALES SUR LE PLAN PROFESSIONNEL
(i) Développement des compétences en matière de technologie dans l'information pour tous les
enseignants
« Tous les enseignants doivent pouvoir maîtriser les nouvelles percées de la technologie et en évaluer les
possibilités d'application dans toutes les formes de l'éducation. Ils doivent également être capables d'évaluer
sous un angle critique les nouveaux auxiliaires techniques. Tous les enseignants en service et tous les
enseignants futurs de tous les types d'écoles et de toutes les disciplines doivent recevoir une formation à la
technologie de l'information... ».
(ii) Les organisations professionnelles des enseignants devraient être en mesure d'exercer une
influence sur cette formation
... « Les syndicats d'enseignants devraient également tenter d'arriver à un accord avec le gouvernement/les
autorités responsables pour concrétiser cette formation ou la faciliter ».
(iii) Chaque direction d'école doit être correctement informée
« Il incombe à la direction des écoles la tâche spécifique de créer dans les écoles une atmosphère
encourageant l'utilisation de la nouvelle technologie ».
(iv) Enseignants responsables de l'introduction et du développement de la technologie de
l'information à l'école
« Il s'agirait de nommer des enseignants volontaires qui auraient spécifiquement pour tâche d'introduire la
technologie de l'information dans leur école et de l'y développer. Ces enseignants devraient être chargés
d'aider, de soutenir et de stimuler leurs collègues afin qu'ils affûtent leur niveau de préparation dans le
secteur de la technologie de l'information».
(v) Une attention particulière doit être accordée au fait que garçons et filles n'ont pas le même point
de départ sur le plan de la technologie de l'information
« Il faut que les écoles prennent conscience du fait que filles et garçons partent souvent de niveaux
différents, au moment où la technologie de l'information est introduite dans des écoles de types différents.
Cette prise de conscience doit s'étendre à toutes les activités de nature éducative».
(vi) Tous les types d'écoles doivent avoir accès à la nouvelle technologie de l'information appropriée à
leurs besoins
« Tous les enseignants doivent avoir accès à la technologie de l'information. Le type de matériel et de
logiciel à introduire pour un programme d'études spécifiques devrait être décidé aux termes de discussions
à l'échelon de l'école »...
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« Le développement de logiciels et de nouvelles techniques pour différents types d'écoles doit toujours se
fonder sur les valeurs éducatives. Le logiciel devrait également être disponible dans la langue maternelle.
La responsabilité des enseignants devrait s'étendre à l'élaboration de logiciels »...
(vii) Le travail dans le secteur de la technologie de l'information à l'échelon international
« L'IE/Europe et le CSEE devraient attirer l'attention sur les questions touchant à la technologie de
l'information dans les enceintes internationales telles que l'UE, l'UNESCO et les organisations
professionnelles européennes »...
(viii) Solidarité entre pays dans la promotion du développement de la technologie de l'information
« L'introduction de la nouvelle technologie menace d'élargir le fossé entre le Nord et le Sud. Pour éviter
cela, il faudrait que les gouvernements, dans le monde entier, soient sensibles à leurs responsabilités
communes et prennent les mesures qui s'imposent pour que le savoir-faire en matière de technologie de
l'information soit transféré à tous les pays ».
4. QUELQUES PERSPECTIVES D'AVENIR
« L'avenir comporte de nombreuses incertitudes, mais deux éléments ne doivent plus être mis en doute sur
le plan du développement social. Le premier est le développement rapide de la technologie de l'information
et le second, qui est à la fois une conséquence et une condition préalable du progrès technique, est la
nécessité du développement des compétences à tous les niveaux de la société. De cette manière,
directement comme indirectement, la technologie de l'information revêtira une importance critique pour les
enseignants et leurs organisations »...
« Les effets plus concrets de l'introduction de la technologie de l'information, de la robotisation et d'autres
innovations techniques sur la société et le secteur de l'éducation sont difficiles à prévoir. Il est toutefois
d'ores et déjà acquis que la structure de la production et de l'organisation des entreprises s'en trouvera
profondément transformée. De nouveaux produits, de nouveaux secteurs de services et de nouvelles
catégories d'emplois se dégagent progressivement. Ces changements ont également des incidences dans le
secteur de l'éducation, du préscolaire ou postsecondaire, ainsi que sur l'éducation des adultes et sur
l'éducation des personnels de manière générale.
S'il est permis au secteur de l'éducation de rester à niveau avec l'utilisation de la technologie moderne, il
pourra bénéficier de retombées positives, qui se répercuteront sur le secteur même mais aussi sur la société
en général. Si au contraire, le secteur de l'éducation est marginalisé sur le plan de la technologie, il courra le
grave danger de perdre son statut, dans chaque pays et sur le plan international ».
... « Les enseignants sont disposés à prendre leurs responsabilités dans le développement de l'éducation, par
exemple en intégrant la nouvelle technologie aux différents types d'écoles suivant un processus
professionnel d'éducation, à condition que les autorités nationales et locales fournissent des ressources en
rapport avec les attentes suscitées ».
« Les personnels des écoles et du secteur de l'éducation sont entrés de plain-pied dans la nouvelle société de
l'information. Cependant, il n'est pas possible, ni souhaitable, de présenter des solutions toutes prêtes. Il
faudrait que les solutions soient évaluées, concrétisées et développées en permanence suivant les conditions
et tâches spécifiques de chaque type d'école et de chaque discipline, lesquelles à leur tour évolueront avec
le temps.
L'introduction de la technologie de l'information ne doit donc jamais devenir un substitut technique facile
aux actions actives, créatives et intellectuelles des êtres humains en vue de développer les connaissances et
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de résoudre les difficultés. Il n'existe pas de liaison directe ou évidente entre le renforcement de la
technologie et l'amélioration de la condition et de la perception des êtres humains ».
... « Ceux qui ne seront pas familiarisés avec les possibilités de la technologie de l'information seront aussi
handicapés que l'étaient, voici cinquante ans, les gens incapables de lire et d'écrire ».
« Mais l'information n'est pas toujours synonyme de connaissance, et l'information instantanée n'implique
pas toujours la connaissance instantanée. L'objectif fondamental de toute l'éducation doit toujours être le
développement de l'individu, envisagé comme être humain. La technologie de l'information élargit
l'éventail des possibilités qui s'offrent à l'enseignant pour différencier et individualiser l'enseignement qu'il
donne ».
... « C'est la manière d'apprendre, la façon dont la connaissance est recherchée et dont les problèmes sont
résolus qui détermineront dans une large mesure la large base nécessaire pour faire des élèves d'aujourd'hui
des citoyens responsables pour demain ».
NDLR : Rien à rajouter sinon que tout cela restera "paroles verbales" si les organisations syndicales
n'interviennent pas énergiquement et en permanence sur les pouvoirs publics pour que les déclarations se
transforment en actes !
Atelier de Travail Interactif en NTIC
Mission
 Aider les haïtiens de partout au processus de développement de leurs communautés respectives en
misant sur la NTIC, l’exigence du 3ème Millénaire.
Objectif Principal
 Compenser les faiblesses de notre système éducatif, fournir un Encadrement Technique aux écoles,
Associations et aux Professionnels.
Objectifs Spécifiques
 Jeter les bases nécessaires pour l’intégration de notre système à la Ligue Internationale de
l’Education Nouvelle (LIEN).
 Résoudre la crise de génération en assurant la transmission de savoir entre les ainés et les
générations montantes
But
 Poser les bases pour l’Université Du Sable de Saint-Marc
Fonctionnement de la Messagerie Electronique or Email
Le courrier électronique, aussi simple soit-il à utiliser, repose sur un fonctionnement plus compliqué que
celui du web. Pour la plupart des utilisateurs son fonctionnement est transparent, ce qui signifie qu'il n'est
pas nécessaire de comprendre comment le courrier électronique fonctionne pour pouvoir l'utiliser.
Néanmoins, la courte introduction ci-dessous permet d'en comprendre le principe et donne les moyens à un
utilisateur de savoir comment configurer au mieux son client de messagerie ou de saisir les mécanismes
fondamentaux du spam.
Intérêt du courrier électronique
Le principe d'utilisation du courrier électronique est relativement simple, c'est ce qui en a rapidement fait le
principal service utilisé sur internet.
A la manière du service postal classique, il suffit de connaître l'adresse de son expéditeur pour lui faire
parvenir un message. Ses deux principaux avantages par rapport au » courrier papier » sont d'une part la
rapidité de transmission du courrier (quasiment instantanée) et le coût réduit (coût global de la connexion à
internet).
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De plus, le courrier électronique permet d'envoyer instantanément un courrier à plusieurs personnes
simultanément.
Dans la pratique, une adresse électronique est souvent de la forme suivante :
[email protected]
Règle de bon usage de la Messagerie
La nétiquette
La nétiquette (contraction des mots « Net » et « éthique ») représente l’ensemble des règles de bon usage
sur internet afin de respecter les autres et d’être respecté.
Il s'agit donc uniquement de règles de civilité et de bonne conduite afin de permettre à l'ensemble des
internautes de partager un comportement respectueux des autres.
Lors de la rédaction et de la transmission d’un message
Indiquer clairement le sujet du message dans la zone « Objet » (ou « Sujet ») Ceci est particulièrement
important pour le destinataire. Il sera d'autant plus facile pour le destinataire de distinguer dans l’ensemble
des courriers qu’il reçoit ceux qui sont prioritaires de ceux qui le sont moins si le sujet du message est
explicite. Cela lui permettra aussi de classer plus facilement les courriers reçus. Il est possible de faire une
distinction entre un sujet général, par convention mis entre crochets (le nom d’un projet par exemple) et
l’énoncé bref du sujet ;
Par exemple : [Projet X] réunion du 13 décembre 2005
N'envoyer le courrier électronique qu'aux personnes concernées- Il est déplacé, et désagréable pour les
destinataires, de transmettre du courrier électronique à n'importe qui. Les destinataires perdent notamment
un temps précieux à trier entre les messages qui les concernent vraiment et ceux qui ont peu ou aucun
intérêt pour eux. Par ailleurs, cette pratique accapare inutilement des ressources du réseau.
Le champ « To : » (ou en français « A : ») désigne le destinataire principal. C’est à lui que s’adresse le
courrier électronique.
Le champ « Cc : » (ou en français « Copie : ») désigne les personnes tenues informées de la
communication par mél.
Le champ « Bcc : » (ou en français « Copie cachée ») désigne des destinataires invisibles de la part de
l’ensemble des autres destinaires. L’utilisation de cette fonctionnalité est déconseillée. On lui préférera
l’acheminement pour information, séparément, de la copie du précédent envoi
Etre bref et bien situer le contexte du message. Pour être lu et bien compris, il est préférable d'utiliser des
phrases courtes et précises. Si le message est long, le diviser en plusieurs paragraphes en facilite la lecture.
Un texte précis et bien structuré permet d’éviter les malentendus ou une mauvaise interprétation. Un
message peut rapidement et facilement être retransmis à d'autres personnes. Utilisez un langage convenable
et évitez l’humour déplacé, les sarcasmes et les injures. Dans le cadre d’un usage professionnel, il est
appréciable pour les destinataires de commencer le message avec une des mentions suivantes :
 Pour information
 Pour avis
 Pour attribution et suite à donner
S'il faut attacher des documents au message, pensez aux destinataires Le destinataire d'un fichier attaché ne
possède pas forcément les logiciels permettant de le lire. Assurez-vous que le fichier est enregistré dans un
format décodable par la plupart des logiciels courants. (ex. .rtf au lieu de .doc). Par ailleurs, faites attention
à la taille des fichiers attachés. Plus la taille est importante, plus le temps de transmission et de réception
sera long. Une pièce jointe volumineuse risque de plus d'être refusée par le serveur de messagerie distant ou
de saturer la boîte du destinataire et ainsi d'empêcher la réception d'autres messages. Utilisez les utilitaires
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compression/décompression pour réduire la taille de ces fichiers (.zip). Avant l’envoi d’un message sensé
contenir une pièce jointe, veillez à ce que la pièce jointe soit bien présente !
Restreindre l'utilisation des caractères en majuscules. Un texte rédigé en majuscules est difficile à lire. Par
ailleurs, l'emploi de mots en majuscules indique, dans les pratiques du Net, que l'on veut exprimer de
grandes émotions (joie, colère), ce qui n'est pas toujours bien ressenti par votre correspondant. Pour faire
ressortir un terme, le placer plutôt entre guillemets.
Avant de transmettre un message, prendre le temps de le relire. Pensez à corriger les fautes de frappe ou de
français. Le style des messages reflète l'image de l'expéditeur.
S'assurer de bien s'identifier et de laisser des coordonnées à la fin du message. Pensez à laisser votre
signature au bas des messages, mais sans prendre trop de place (4 ou 5 lignes au maximum), en précisant
par exemple votre fonction, votre entité de rattachement. Les coordonnées téléphoniques peuvent être utiles
si un de vos destinataires cherchent à vous joindre rapidement. La coutume veut que la signature soit
précédée d'une ligne contenant simplement deux tirets (« -- »).
Utilisation du courrier
Un client de messagerie, logiciel permettant de rédiger, consulter et envoyer ses courriers électronique, est
généralement composé d'un certain nombre de fenêtres. Les fenêtres principales d'un tel logiciel sont
généralement les suivantes :
Arrivée, Entrée, Boîte de réception (en anglais In, Incoming) : elle représente la boîte de réception
principale du courrier,
Éléments envoyés, Boîte d'envoi (Out, Sent) : ce sont les copies des messages que vous avez envoyés
éléments supprimés, Corbeille ou Poubelle (Deleted, Trash) : il s'agit de la poubelle, c'est-à-dire du
dossier contenant les courriers électroniques supprimés. Lorsque les courriers apparaissent dans la
poubelle, il est encore possible de les récupérer. Pour les supprimer définitivement, il est nécessaire de
vider (purger) la corbeille,
Dossiers (Folders) : la plupart des outils permettent de classer les courriers par dossier, à la manière des
répertoires du disque dur.
Champs de courrier électronique
Voici la signification des champs à remplir lorsque vous envoyez un mail :
De (From) : c'est votre adresse électronique, la plupart du temps vous n'aurez pas à remplir ce champ car il
est généralement défini par le client de messagerie selon vos préférences
A (To) : ce champ correspond à l'adresse électronique du destinataire
Objet (Subject) : il s'agit du titre que votre destinataire verra lorsqu'il voudra lire le courrier
Cc (Copie Carbone) : cela permet d'envoyer un mail à de nombreuses personnes en écrivant leurs adresses
respectives séparées par des virgules
Bcc (Blind Carbon Copy, traduisez Copie Carbone Invisible, notée Cci, parfois Copie cachée) : il s'agit
d'une simple Copie Carbone à la différence près que le destinataire ne voit pas dans l'en-tête la liste des
personnes en copie cachée
Message : il s'agit du corps du votre courrier
La fonction Copie Carbone permet de mettre en copie des personnes non concernées directement par le
message et que vous souhaitez mettre au courant du contenu du message ou bien du fait même d'avoir
envoyé le courrier au(x) destinataire(s).
La fonction Copie Carbone Invisible permet de mettre en copie des personnes sans que quiconque des
destinataires ou bien des destinataires cachés ne voient qu'ils sont en copie. Il est généralement
recommandé lors de l'envoi de mail à de nombreuses personnes de les mettre en Copie Carbone Invisible
afin d'éviter qu'un des destinataires ne réponde à tout le monde ou bien ne constitue une liste d'adresses.
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Les autres fonctions de la messagerie sont notamment :
Fichier attaché, Pièces jointes (Attached Files, Attachments) : il est possible d'attacher un fichier à un
courrier en précisant son emplacement sur le disque dur
Signature : si le client de messagerie le permet, il est souvent possible de définir une signature, c'est-à-dire
quelques lignes de texte qui seront ajoutées à la fin du courrier.
How Computer Work
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How BIOS Works
How Caching Works
How RAM Works
How Microprocessors Work
How Computer Memory Works
How Microcontrollers Work
How AGP Works
How IDE Controllers Work
How PCI-Express Works
How PCI Works
How SCSI Works
How USB Ports Work
How Sound Cards Work
How PCs Work
More Great Links
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Basic Computer Operation Tutorial
How Motherboards Are Made
The History of the Computer
Computer History Museum
Memory Architectures
How Power Supply works
If there is any one component that is absolutely vital to the operation of a computer, it is the power supply.
Without it, a computer is just an inert box full of plastic and metal. The power supply converts the alternating
current (AC) line from your home to the direct current (DC) needed by the personal computer. In this article,
we'll learn how PC power supplies work and what the wattage ratings mean.
Power Supply
In a personal computer (PC), the power supply is the metal box usually found in a corner of the case. The
power supply is visible from the back of many systems because it contains the power-cord receptacle and the
cooling fan
Power supplies, often referred to as "switching power supplies", use switcher technology to convert the AC
input to lower DC voltages. The typical voltages supplied are:
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3.3 volts
5 volts
12 volts
The 3.3- and 5-volts are typically used by digital circuits, while the 12-volt is used to run motors in disk drives
and fans. The main specification of a power supply is in watts. A watt is the product of the voltage in volts and
the current in amperes or amps. If you have been around PCs for many years, you probably remember that the
original PCs had large red toggle switches that had a good bit of heft to them. When you turned the PC on or
off, you knew you were doing it. These switches actually controlled the flow of 120 volt power to the power
supply.
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Today you turn on the power with a little push button, and you turn off the machine with a menu option. These
capabilities were added to standard power supplies several years ago. The operating system can send a signal
to the power supply to tell it to turn off. The push button sends a 5-volt signal to the power supply to tell it when
to turn on. The power supply also has a circuit that supplies 5 volts, called VSB for "standby voltage" even
when it is officially "off", so that the button will work.
Switcher Technology
Prior to 1980 or so, power supplies tended to be heavy and bulky. They used large, heavy transformers and
huge capacitors (some as large as soda cans) to convert line voltage at 120 volts and 60 hertz into 5 volts and
12 volts DC.
The switching power supplies used today are much smaller and lighter. They convert the 60-Hertz (Hz, or
cycles per second) current to a much higher frequency, meaning more cycles per second. This conversion
enables a small, lightweight transformer in the power supply to do the actual voltage step-down from 110 volts
(or 220 in certain countries) to the voltage needed by the particular computer component. The higher-frequency
AC current provided by a switcher supply is also easier to rectify and filter compared to the original 60-Hz AC
line voltage, reducing the variances in voltage for the sensitive electronic components in the computer.
A switcher power supply draws only the power it needs from the AC line. The typical voltages and current
provided by a power supply are shown on the label on a power supply.
Switcher technology is also used to make AC from DC, as found in many of the automobile power inverters
used to run AC appliances in an automobile and in uninterruptible power supplies. Switcher technology in
automotive power inverters changes the direct current from the auto battery into alternating current. The
transformer uses alternating current to make the transformer in the inverter step the voltage up to that of
household appliances (120 VAC).
Power Supply Standardization
Over time, there have been at least six different standard power supplies for personal computers. Recently, the
industry has settled on using ATX-based power supplies. ATX is an industry specification that means the power
supply has the physical characteristics to fit a standard ATX case and the electrical characteristics to work with
an ATX motherboard.
PC power-supply cables use standardized, keyed connectors that make it difficult to connect the wrong ones.
Also, fan manufacturers often use the same connectors as the power cables for disk drives, allowing a fan to
easily obtain the 12 volts it needs. Color-coded wires and industry standard connectors make it possible for the
consumer to have many choices for a replacement power supply.
Advanced Power Management
Advanced Power Management (APM) offers a set of five different states that your system can be in. It was
developed by Microsoft and Intel for PC users who wish to conserve power. Each system component, including
the operating system, basic input/output system (BIOS), motherboard and attached devices all need to be
APM-compliant to be able to use this feature. Should you wish to disable APM because you suspect it is using
up system resources or causing a conflict, the best way to do this is in the BIOS. That way, the operating
system won't try to reinstall it, which could happen if it were disabled only in the software.
Power Supply Wattage
A 400-watt switching power supply will not necessarily use more power than a 250-watt supply. A larger supply
may be needed if you use every available slot on the motherboard or every available drive bay in the personal
computer case. It is not a good idea to have a 250-watt supply if you have 250 watts total in devices, since the
supply should not be loaded to 100 percent of its capacity.
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According to PC Power & Cooling, Inc., some power consumption values (in watts) for common items in a
personal computer are:
PC Item
Watts
Accelerated Graphics Port (AGP) card
20 to 30W
Peripheral Component Interconnect (PCI) card
5W
Small computer system interface (SCSI) PCI card
20 to 25W
Floppy Disk Drive
5W
Network Interface Card
4W
50X CD-ROM drive
10 to 25W
RAM
10W per 128M
5200 RPM Integrated Drive Electronics (IDE) hard disk drive
5 to 11W
7200 RPM IDE hard disk drive
5 to 15W
Motherboard (without CPU or RAM)
20 to 30W
550 MHz Pentium III
30W
733 MHz Pentium III
23.5W
300 MHz Celeron
18W
600 MHz Athlon
45W
Power supplies of the same form factor ("form factor" refers to the actual shape of the motherboard) are
typically differentiated by the wattage they supply and the length of the warranty.
Power Supply Problems
The PC power supply is probably the most failure-prone item in a personal computer. It heats and cools each
time it is used and receives the first in-rush of AC current when the PC is switched on. Typically, a stalled
cooling fan is a predictor of a power supply failure due to subsequent overheated components. All devices in a
PC receive their DC power via the power supply.
A typical failure of a PC power supply is often noticed as a burning smell just before the computer shuts down.
Another problem could be the failure of the vital cooling fan, which allows components in the power supply to
overheat. Failure symptoms include random rebooting or failure in Windows for no apparent reason.
For any problems you suspect to be the fault of the power supply, use the documentation that came with your
computer. If you have ever removed the case from your personal computer to add an adapter card or memory,
you can change a power supply. Make sure you remove the power cord first, since voltages are present even
though your computer is off.
Power Supply Improvements
Recent motherboard and chipset improvements permit the user to monitor the revolutions per minute (RPM) of
the power supply fan via BIOS and a Windows application supplied by the motherboard manufacturer. New
designs offer fan control so that the fan only runs the speed needed, depending on cooling needs.
Recent designs in Web servers include power supplies that offer a spare supply that can be exchanged while
the other power supply is in use. Some new computers, particularly those designed for use as servers, provide
redundant power supplies. This means that there are two or more power supplies in the system, with one
providing power and the other acting as a backup. The backup supply immediately takes over in the event of a
failure by the primary supply. Then, the primary supply can be exchanged while the other power supply is in
use.
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Is it better to turn my computer off when I am not using it or leave it on all the time?
This is one of those questions where there is no single right answer. In other words, it depends on how you use
your computer.
There are at least three situations that force you to leave your computer on 24 hours a day:
 You are on a network, and the network administrators back up files and/or upgrade software over
the network at night. If that is the case, and you want your machine backed up or upgraded, then
you need to leave it on all the time.
 You are using your machine as some sort of server. For example, HowStuffWorks has a machine
that creates the images for the How Webcams Work article. It needs to be on 24 hours a day. If
your machine acts as a file server, print server, Web server, etc., on a LAN (local area network) or
the Internet, then you need to leave it on all the time.
 If you are running something like SETI@home and you want to produce as many result sets as
possible, you need to leave your machine on all the time.
If you do not fall into any of these categories, then you have a choice about whether or not to leave your
machine on.
One reason why you might want to turn it off is economic. A typical PC consumes something like 300 watts.
Let's assume that you use your PC for four hours every day, so the other 20 hours it is on would be wasted
energy. If electricity costs 10 cents per kilowatt-hour in your area, then that 20 hours represents 60 cents a day.
Sixty cents a day adds up to $219 per year.
It's possible to use the energy-saving features build into modern machines and cut that figure in half. For
example, you can have the monitor and hard disk power down automatically when not in use. You'll still be
wasting $100 per year.
The argument for leaving your computer on all the time is that turning it on and off somehow stresses the
computer's components. For example, when the CPU chip is running, it can get quite hot, and when you turn
the machine off it cools back down. The expansion and contraction from the heat probably has some effect on
the solder joints holding the chip in place, and on the micro-fine details on the chip itself. But here are three
ways to look at that:
 If it were a significant problem, then machines would be failing all the time. In fact, hardware is very
reliable (software is a whole different story, and there is a lot to be said for rebooting every day).
 I don't know a single person who leaves the TV on 24 hours a day. TVs contain many of the same
components that computers do. TVs certainly have no problems being cycled on and off.
 Most vendors will sell you a three-year full-replacement warrantee for about $150. If you are worried
about it, spend some of the money you are saving by turning your machine off and buy a service
contract. Over three years, you come out way ahead!
Leave the System On or Turn it Off? (Thermal Stress vs. Wearout)
One of the endless debates in the computer world, along with such controversies as the use of parity
memory or the choice of IDE vs. SCSI, is the question of whether or not, and for how long, a PC should be
left running when it is not in use. This section takes a look at this matter and explains the issues so you can
decide what is sensible for you and make a decision on your policy for your equipment.
The basic question is: you have a PC on your desk at the office. You use it all day. When you go home for
the night, should you turn off the PC or leave it running? This is not a simple question to answer because
there are so many different factors involved in the decision in most cases. And the decision also depends on
the type of PC: a high-end server is more likely to be left on 24 hours a day than a PC used twice a week at
home:
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Convenience: For many people who run multiple applications at a time, having to reboot the PC
every morning is a pain in the rear end. It can take me a good 10 minutes in the morning to boot my
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machine and get my working environment set up the way I like it. Also, I like to run maintenance
tasks during the day while I am at work. I will concede that not turning off the PC because you don't
want to restart all your applications may be laziness on my part, but it is a significant reason why
many people leave their machines on overnight.
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Power Consumption: Leaving your PC running when you are not using it wastes electricity. That's
a fact, so I won't sugar-coat it. On the other hand, it doesn't waste that much electricity, if you leave
the monitor off (which you should be doing anyway). You can also use power management to
reduce the amount of electricity used during idle periods.
Thermal Stress: After your PC has been off for many hours the components will be at room
temperature. When the PC is turned on, the components will heat up, sometimes to much higher
temperatures than 70 degrees F, causing them to expand. Then when you turn off the PC they cool
down again, and contract. This cycle of heating and cooling causes thermal stress in the
components that make up the PC, and is a leading cause of system failure (this is also what
normally causes light bulbs to fail, which is why they usually pop when you turn them on, and not
out of the blue). Leaving the PC on all the time greatly reduces thermal stress, which can lead to
increased life for the system. Strange as it may seem, most components last longer if you leave then
running 24 hours a day for years than if you leave them off for 22 hours a day and on for only 2 (but
this isn't true of all components.)
Wearout: The opposite factor to thermal stress is wearout. While leaving the PC on all the time
reduces thermal stress and hence prolongs system life, it also causes components to wear out more
quickly. This is more of a factor for some components than others--especially monitors.
Cooling: It is important to remember that some office buildings run with automated thermostats
that turn off the air conditioning at night; if it's 95 during the day and 80 at night, the PC will be
quite warm in the morning when the power comes on. In this case you may be risking the system
overheating by leaving it running at night.
Risk of Power Interruption: Leaving your PC on for long periods of time exposes it to the
potential risk of power spikes and surges, brownouts, blackouts and other problems. If you are using
a good-quality UPS then this is not really a factor, although remember that unless your UPS
supports power-down signaling to shut down the machine, a one-hour blackout will result in about
the same abrupt shut-off of your machine, just a few minutes later than it would without a UPS. If
you are not using a UPS, and you are in an area prone to power problems, leaving the machine on
all the time may be unwise (you should be using a good power conditioning device if this is the
case, anyway).
You need to decide for yourself what decisions you want to make about your PCs. My personal stance on
the matter has changed over time based on my computing habits and as I have learned more. I now have a
basic policy of turning off the PC if I feel that I will not be using it in the next 24 hours. At work, I leave
my PC on overnight during the week, but I turn it off over the weekend or when I am out of the office. At
home, I usually leave my PC on all the time; I use it every evening and during the day on weekends, I run
backups overnight, and I have automatic maintenance tasks that run during the day on weekdays.
Remember that I live in New England; if I lived in South Florida and had no UPS, I might reconsider this
policy due to the electrical storm activity, for example.
For me, this makes sense, and I acknowledge the tradeoffs I make in doing this. I greatly reduce the thermal
stress on my main system and hard disks, but I increase the chance of wearout of these components. I keep
the monitor off for safety and to prevent wearout. I also realize that I am spending some money on
electricity to keep the system going all the time but it is worth it to me to do this.
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Warning: There is one thing I feel rather strongly about in this matter--monitors should be turned off at
night, both to prolong the life of the equipment and for safety reasons as well. This subject is discussed in
more detail in the care section on monitors.
How PCs Work
When you mention the word "technology," most people think about computers. Virtually every facet of our lives
has some computerized component. The appliances in our homes have microprocessors built into them, as do
our televisions. Even our cars have a computer. But the computer that everyone thinks of first is typically the
personal computer, or PC.
How Microprocessors Work
The computer you are using to read this page uses a microprocessor to do its work. The microprocessor is
the heart of any normal computer, whether it is a desktop machine, a server or a laptop. The microprocessor
you are using might be a Pentium, a K6, a PowerPC, a Sparc or any of the many other brands and types of
microprocessors, but they all do approximately the same thing in approximately the same way.
A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is
fabricated on a single chip. The first microprocessor was the Intel 4004, introduced in 1971. The 4004 was not
very powerful -- all it could do was add and subtract, and it could only do that 4 bits at a time. But it was
amazing that everything was on one chip. Prior to the 4004, engineers built computers either from collections of
chips or from discrete components (transistors wired one at a time). The 4004 powered one of the first portable
electronic calculators.
If you have ever wondered what the microprocessor in your computer is doing, or if you have ever wondered
about the differences between types of microprocessors, then read on. In this article, you will learn how fairly
simple digital logic techniques allow a computer to do its job, whether its playing a game or spell checking a
document!
Intel 4004 chip
Microprocessor Progression: Intel
The first microprocessor to make it into a home computer was the Intel 8080, a
complete 8-bit computer on one chip, introduced in 1974. The first microprocessor to
make a real splash in the market was the Intel 8088, introduced in 1979 and
incorporated into the IBM PC (which first appeared around 1982). If you are familiar
with the PC market and its history, you know that the PC market moved from the 8088
to the 80286 to the 80386 to the 80486 to the Pentium to the Pentium II to the
Pentium III to the Pentium 4. All of these microprocessors are made by Intel and all of
them are improvements on the basic design of the 8088. The Pentium 4 can execute
any piece of code that ran on the original 8088, but it does it about 5,000 times faster! Intel 8080
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The following table helps you to understand the differences between the different processors that Intel has
introduced over the years.
MIPS
Name
Date
Transistors Microns Clock speed Data width
8080
1974
6,000
6
2 MHz
8 bits
0.64
8088
1979
29,000
3
5 MHz
16 bits / 8-bit bus
0.33
80286
1982
134,000
1.5
6 MHz
16 bits
1
80386
1985
275,000
1.5
16 MHz
32 bits
5
80486
1989
1,200,000
1
25 MHz
32 bits
20
Pentium
1993
3,100,000
0.8
60 MHz
32 bits / 64-bit bus
100
Pentium II
1997
7,500,000
0.35
233 MHz
32 bits / 64-bit bus
~300
Pentium III
1999
9,500,000
0.25
450 MHz
32 bits / 64-bit bus
~510
Pentium 4
2000
42,000,000
0.18
1.5 GHz
32 bits / 64-bit bus
~1,700
Pentium 4 "Prescott"
2004
125,000,000
0.09
3.6 GHz
32 bits / 64-bit bus
~7,000
Information about this table:
What's a Chip?
A chip is also called an integrated circuit. Generally it is a small, thin piece of silicon onto which the transistors
making up the microprocessor have been etched. A chip might be as large as an inch on a side and can contain tens
of millions of transistors. Simpler processors might consist of a few thousand transistors etched onto a chip just a few
millimeters square.
 The date is the year that the processor was first introduced. Many processors are re-introduced at
higher clock speeds for many years after the original release date.
 Transistors is the number of transistors on the chip. You can see that the number of transistors on
a single chip has risen steadily over the years.
 Microns is the width, in microns, of the smallest wire on the chip. For comparison, a human hair is
100 microns thick. As the feature size on the chip goes down, the number of transistors rises.
 Clock speed is the maximum rate that the chip can be clocked at. Clock speed will make more
sense in the next section.
 Data Width is the width of the ALU. An 8-bit ALU can add/subtract/multiply/etc. two 8-bit numbers,
while a 32-bit ALU can manipulate 32-bit numbers. An 8-bit ALU would have to execute four
instructions to add two 32-bit numbers, while a 32-bit ALU can do it in one instruction. In many
cases, the external data bus is the same width as the ALU, but not always. The 8088 had a 16-bit
ALU and an 8-bit bus, while the modern Pentiums fetch data 64 bits at a time for their 32-bit ALUs.
 MIPS stands for "millions of instructions per second" and is a rough measure of the performance of a
CPU. Modern CPUs can do so many different things that MIPS ratings lose a lot of their meaning,
but you can get a general sense of the relative power of the CPUs from this column.
From this table you can see that, in general, there is a relationship between clock speed and MIPS. The
maximum clock speed is a function of the manufacturing process and delays within the chip. There is also a
relationship between the number of transistors and MIPS. For example, the 8088 clocked at 5 MHz but only
executed at 0.33 MIPS (about one instruction per 15 clock cycles). Modern processors can often execute at a
rate of two instructions per clock cycle. That improvement is directly related to the number of transistors on the
chip and will make more sense in the next section.
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Microprocessor Logic
To understand how a microprocessor works, it is helpful to look inside
and learn about the logic used to create one. In the process you can
also learn about assembly language -- the native language of a
microprocessor -- and many of the things that engineers can do to
boost the speed of a processor.
A microprocessor executes a collection of machine instructions that
tell the processor what to do. Based on the instructions, a
microprocessor does three basic things:
 Using its ALU (Arithmetic/Logic Unit), a microprocessor can
perform mathematical operations like addition, subtraction,
multiplication and division. Modern microprocessors contain
Photo courtesy Intel Corporation
complete floating point processors that can perform
Intel Pentium 4 processor
extremely sophisticated operations on large floating point
numbers.
 A microprocessor can move data from one memory location to another.
 A microprocessor can make decisions and jump to a new set of instructions based on those
decisions.
There may be very sophisticated things that a microprocessor does, but those are its three basic activities. The
following diagram shows an extremely simple microprocessor capable of doing those three things:
This is about as simple as a microprocessor gets. This microprocessor has:
 An address bus (that may be 8, 16 or 32 bits wide) that sends an address to memory
 A data bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from
memory
 An RD (read) and WR (write) line to tell the memory whether it wants to set or get the addressed
location
 A clock line that lets a clock pulse sequence the processor
 A reset line that resets the program counter to zero (or whatever) and restarts execution
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Let's assume that both the address and data buses are 8 bits wide in this example.
Here are the components of this simple microprocessor:
 Registers A, B and C are simply latches made out of flip-flops. (See the section on "edge-triggered
latches" in How Boolean Logic Works for details.)
 The address latch is just like registers A, B and C.
 The program counter is a latch with the extra ability to increment by 1 when told to do so, and also to
reset to zero when told to do so.
 The ALU could be as simple as an 8-bit adder (see the section on adders in How Boolean Logic
Works for details), or it might be able to add, subtract, multiply and divide 8-bit values. Let's
assume the latter here.
 The test register is a special latch that can hold values from comparisons performed in the ALU. An
ALU can normally compare two numbers and determine if they are equal, if one is greater than the
other, etc. The test register can also normally hold a carry bit from the last stage of the adder. It
stores these values in flip-flops and then the instruction decoder can use the values to make
decisions.
 There are six boxes marked "3-State" in the diagram. These are tri-state buffers. A tri-state buffer
can pass a 1, a 0 or it can essentially disconnect its output (imagine a switch that totally
disconnects the output line from the wire that the output is heading toward). A tri-state buffer
allows multiple outputs to connect to a wire, but only one of them to actually drive a 1 or a 0 onto
the line.
 The instruction register and instruction decoder are responsible for controlling all of the other
components.
Although they are not shown in this diagram, there would be control lines from the instruction decoder that
would:
 Tell the A register to latch the value currently on the data bus
 Tell the B register to latch the value currently on the data bus
 Tell the C register to latch the value currently output by the ALU
 Tell the program counter register to latch the value currently on the data bus
 Tell the address register to latch the value currently on the data bus
 Tell the instruction register to latch the value currently on the data bus
 Tell the program counter to increment
 Tell the program counter to reset to zero
 Activate any of the six tri-state buffers (six separate lines)
 Tell the ALU what operation to perform
 Tell the test register to latch the ALU's test bits
 Activate the RD line
 Activate the WR line
Coming into the instruction decoder are the bits from the test register and the clock line, as well as the bits from
the instruction register.
A PC is a general purpose tool built around a microprocessor. It has lots of different parts -- memory, a hard
disk, a modem, etc. -- that work together. "General purpose" means that you can do many different things with
a PC. You can use it to type documents, send e-mail, browse the Internet and play games.
In this article, we will talk about PCs in the general sense and all the different parts that go into them. You will
learn about the various components and how they work together in a basic operating session. You'll also find
out what the future may hold for these machines.
Let's take a look at the main components of a typical desktop computer.
 Central processing unit (CPU) - The microprocessor "brain" of the computer system is called the
central processing unit. Everything that a computer does is overseen by the CPU.
 Memory - This is very fast storage used to hold data. It has to be fast because it connects directly to
the microprocessor. There are several specific types of memory in a computer:
 Random-access memory (RAM) - Used to temporarily store information that the
computer is currently working with
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Read-only memory (ROM) - A permanent type of memory storage used by the
computer for important data that does not change
Basic input/output system (BIOS) - A type of ROM that is used by the computer to
establish basic communication when the computer is first turned on
Caching - The storing of frequently used data in extremely fast RAM that connects
directly to the CPU
Virtual memory - Space on a hard disk used to temporarily store data and swap it in
and out of RAM as needed
 Motherboard - This is the main circuit board that all of the other internal components connect to. The
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CPU and memory are usually on the motherboard. Other systems may be found directly on the
motherboard or connected to it through a secondary connection. For example, a sound card can
be built into the motherboard or connected through PCI.
Power supply - An electrical transformer regulates the electricity used by the computer.
Hard disk - This is large-capacity permanent storage used to hold information such as programs and
documents.
Operating system - This is the basic software that allows the user to interface with the computer.
Integrated Drive Electronics (IDE) Controller - This is the primary interface for the hard drive, CDROM and floppy disk drive.
Peripheral Component Interconnect (PCI) Bus - The most common way to connect additional
components to the computer, PCI uses a series of slots on the motherboard that PCI cards plug
into.
SCSI - Pronounced "scuzzy," the small computer system interface is a method of adding
additional devices, such as hard drives or scanners, to the computer.
AGP - Accelerated Graphics Port is a very high-speed connection used by the graphics card to
interface with the computer.
Sound card - This is used by the computer to record and play audio by converting analog sound into
digital information and back again.
Graphics card - This translates image data from the computer into a format that can be displayed by
the monitor.
In the next section, we'll look at how your computer connects to the outside world.
How Motherboards Work
If you've ever taken the case off of a computer, you've seen the one piece of equipment that ties everything
together -- the motherboard. A motherboard allows all the parts of your computer to receive power and
communicate with one another.
Motherboards have come a long way in the last twenty years. The first motherboards held very few actual
components. The first IBM PC motherboard had only a processor and card slots. Users plugged components
like floppy drive controllers and memory into the slots.
Today, motherboards typically boast a wide variety of built-in features, and they directly affect a computer's
capabilities and potential for upgrades. In this article, we'll look at the general components of a motherboard.
Then, we'll closely examine five points that dramatically affect what a computer can do.
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Photo courtesy HowStuffWorks Shopper
A modern motherboard
A motherboard by itself is useless, but a computer has to have one to operate. The motherboard's main job is
to hold the computer's microprocessor chip and let everything else connect to it. Everything that runs the
computer or enhances its performance is either part of the motherboard or plugs into it via a slot or port.
The shape and layout of a motherboard is called the form factor. The form factor affects where individual
components go and the shape of the computer's case. There are several specific form factors that most PC
motherboards use so that they can all fit in standard cases. For a comparison of form factors, past and present,
check out Motherboards.org.
The form factor is just one of the many standards that apply to motherboards. Some of the other standards
include:
 The socket for the microprocessor determines what kind of Central Processing Unit (CPU) the
motherboard uses.
 The chipset is part of the motherboard's logic system and is usually made of two parts -- the
northbridge and the southbridge. These two "bridges" connect the CPU to other parts of the
computer.
 The Basic Input/Output System (BIOS) chip controls the most basic functions of the computer and
performs a self-test every time you turn it on. Some systems feature dual BIOS, which provides a
backup in case one fails or in case of error during updating.
 The real time clock chip is a battery-operated chip that maintains basic settings and the system
time.
The slots and ports found on a motherboard include:
 Peripheral Component Interconnect (PCI)- connections for video, sound and video capture cards, as
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well as network cards
Accelerated Graphics Port (AGP) - dedicated port for video cards.
Integrated Drive Electronics (IDE) - interfaces for the hard drives
Universal Serial Bus or FireWire - external peripherals
Memory slots
Some motherboards also incorporate newer technological advances:
 Redundant Array of Independent Discs (RAID) controllers allow the computer to recognize multiple
drives as one drive.
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 PCI Express is a newer protocol that acts more like a network than a bus. It can eliminate the need
for other ports, including the AGP port.
 Rather than relying on plug-in cards, some motherboards have on-board sound, networking, video
or other peripheral support.
Photo courtesy HowStuffWorks Shopper
A Socket 754 motherboard
Many people think of the CPU as one of the most important parts of a computer. We'll look at how it affects the
rest of the computer in the next section.
Sockets and CPUs
The CPU is the first thing that comes to mind when many people think about a computer's speed and
performance. The faster the processor, the faster the computer can think. In the early days of PC computers, all
processors had the same set of pins that would connect the CPU to the motherboard, called the Pin Grid Array
(PGA). These pins fit into a socket layout called Socket 7. This meant that any processor would fit into any
motherboard.
Photo courtesy HowStuffWorks Shopper
A Socket 939 motherboard
Today, however, CPU manufacturers Intel and AMD use a variety of PGAs, none of which fit into Socket 7. As
microprocessors advance, they need more and more pins, both to handle new features and to provide more
and more power to the chip.
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Current socket arrangements are often named for the number of pins in the PGA. Commonly used sockets are:
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Socket 478 - for older Pentium and Celeron processors
Socket 754 - for AMD Sempron and some AMD Athlon processors
Socket 939 - for newer and faster AMD Athlon processors
Socket AM2 - for the newest AMD Athlon processors
Socket A - for older AMD Athlon processors
Photo courtesy HowStuffWorks Shopper
A Socket LGA755 motherboard
The newest Intel CPU does not have a PGA. It has an LGA, also known as Socket T. LGA stands for Land Grid
Array. An LGA is different from a PGA in that the pins are actually part of the socket, not the CPU.
Anyone who already has a specific CPU in mind should select a motherboard based on that CPU. For example,
if you want to use one of the new multi-core chips made by Intel or AMD, you will need to select a motherboard
with the correct socket for those chips. CPUs simply will not fit into sockets that don't match their PGA.
The CPU communicates with other elements of the motherboard through a chipset. We'll look at the chipset in
more detail next.
Chipsets
The chipset is the "glue" that connects the microprocessor to the rest of the motherboard and therefore to the
rest of the computer. On a PC, it consists of two basic parts -- the northbridge and the southbridge. All of the
various components of the computer communicate with the CPU through the chipset.
Photo courtesy HowStuffWorks Shopper
The northbridge and southbridge
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The northbridge connects directly to the processor via the front side bus (FSB). A memory controller is located
on the northbridge, which gives the CPU fast access to the memory. The northbridge also connects to the AGP
or PCI Express bus and to the memory itself.
The southbridge is slower than the northbridge, and information from the CPU has to go through the
northbridge before reaching the southbridge. Other busses connect the southbridge to the PCI bus, the USB
ports and the IDE or SATA hard disk connections.
Chipset selection and CPU selection go hand in hand, because manufacturers optimize chipsets to work with
specific CPUs. The chipset is an integrated part of the motherboard, so it cannot be removed or upgraded. This
means that not only must the motherboard's socket fit the CPU, the motherboard's chipset must work optimally
with the CPU.
Next, we'll look at busses, which, like the chipset, carry information from place to place.
Bus Speed
A bus is simply a circuit that connects one part of the motherboard to another. The more data a bus can handle
at one time, the faster it allows information to travel. The speed of the bus, measured in megahertz (MHz),
refers to how much data can move across the bus simultaneously.
Busses connect different parts of the motherboard
to one another
Bus speed usually refers to the speed of the front side bus (FSB), which connects the CPU to the northbridge.
FSB speeds can range from 66 MHz to over 800 MHz. Since the CPU reaches the memory controller though
the northbridge, FSB speed can dramatically affect a computer's performance.
Here are some of the other busses found on a motherboard:
 The back side bus connects the CPU with the level 2 (L2) cache, also known as secondary or
external cache. The processor determines the speed of the back side bus.
 The memory bus connects the northbridge to the memory.
 The IDE or ATA bus connects the southbridge to the disk drives.
 The AGP bus connects the video card to the memory and the CPU. The speed of the AGP bus is
usually 66 MHz.
 The PCI bus connects PCI slots to the southbridge. On most systems, the speed of the PCI bus is
33 MHz. Also compatible with PCI is PCI Express, which is much faster than PCI but is still
21
compatible with current software and operating systems. PCI Express is likely to replace both PCI
and AGP busses.
The faster a computer's bus speed, the faster it will operate -- to a point. A fast bus speed cannot make up for a
slow processor or chipset.
Now let's look at memory and how it affects the motherboard's speed.
Memory and Other Features
We've established that the speed of the processor itself controls how quickly a computer thinks. The speed of
the chipset and busses controls how quickly it can communicate with other parts of the computer. The speed of
the RAM connection directly controls how fast the computer can access instructions and data, and therefore
has a big effect on system performance. A fast processor with slow RAM is going nowhere.
The amount of memory available also controls how much data the computer can have readily available. RAM
makes up the bulk of a computer's memory. The general rule of thumb is the more RAM the computer has, the
better.
Photo courtesy HowStuffWorks Shopper
184-pin DDR DIMM RAM
Much of the memory available today is dual data rate (DDR) memory. This
means that the memory can transmit data twice per cycle instead of once,
which makes the memory faster. Also, most motherboards have space for
multiple memory chips, and on newer motherboards, they often connect to the
northbridge via a dual bus instead of a single bus. This further reduces the
amount of time it takes for the processor to get information from the memory.
RAM
For information about different
types of RAM, check out How
RAM Works.
22
Photo courtesy HowStuffWorks Shopper
200-pin DDR SODIMM RAM
A motherboard's memory slots directly affect what kind and how much memory is supported. Just like other
components, the memory plugs into the slot via a series of pins. The memory module must have the right
number of pins to fit into the slot on the motherboard.
In the earliest days of motherboards, virtually everything other than the
processor came on a card that plugged into the board. Now, motherboards
feature a variety of onboard accessories such as LAN support, video, sound
support and RAID controllers.
Motherboards with all the bells and whistles are convenient and simple to
install. There are motherboards that have everything you need to create a
complete computer -- all you do is stick the motherboard in a case and add a
hard disk, a CD drive and a power supply. You have a completely operational
computer on a single board.
Photo courtesy HowStuffWorks Shopper
For many average users, these built-in features provide ample support for
64MB SDRAM SIMM
video and sound. For avid gamers and people who do high-intensity graphic
or computer-aided design (CAD) work, however, separate video cards provide much better performance.
For more information on motherboards and related topics, check out the links on the following page.
How RAM Works
Random access memory (RAM) is the best known form of computer memory. RAM is considered "random
access" because you can access any memory cell directly if you know the row and column that intersect at that
cell.
The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can
only be accessed sequentially (like a cassette tape). If the data is not in the current location, each memory cell
is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally
stored in the order in which it will be used (a good example is the texture buffer memory on a video card). RAM
data, on the other hand, can be accessed in any order.
In this article, you'll learn all about what RAM is, what kind you should buy and how to install it.
Dynamic RAM
Similar to a microprocessor, a memory chip is an integrated circuit (IC) made of millions of transistors and
capacitors. In the most common form of computer memory, dynamic random access memory (DRAM), a
transistor and a capacitor are paired to create a memory cell, which represents a single bit of data. The
capacitor holds the bit of information -- a 0 or a 1 (see How Bits and Bytes Work for information on bits). The
transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its
state.
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A capacitor is like a small bucket that is able to store electrons. To store a 1 in the memory cell, the bucket is
filled with electrons. To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a
matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the
CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they
discharge. To do this, the memory controller reads the memory and then writes it right back. This refresh
operation happens automatically thousands of times per second.
The capacitor in a dynamic RAM memory cell is like a leaky bucket.
It needs to be refreshed periodically or it will discharge to 0.
This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed
all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows
down the memory.
Memory cells are etched onto a silicon wafer in an array of columns (bitlines) and rows (wordlines). The
intersection of a bitline and wordline constitutes the address of the memory cell.
Memory is made up of bits arranged in a two-dimensional grid.
In this figure, red cells represent 1s and white cells represent 0s.
In the animation, a column is selected and then rows are charged to write data into the specific column.
DRAM works by sending a charge through the appropriate column (CAS) to activate the transistor at each bit in
the column. When writing, the row lines contain the state the capacitor should take on. When reading, the
sense-amplifier determines the level of charge in the capacitor. If it is more than 50 percent, it reads it as a 1;
otherwise it reads it as a 0. The counter tracks the refresh sequence based on which rows have been accessed
in what order. The length of time necessary to do all this is so short that it is expressed in nanoseconds
(billionths of a second). A memory chip rating of 70ns means that it takes 70 nanoseconds to completely read
and recharge each cell.
Memory cells alone would be worthless without some way to get information in and out of them. So the memory
cells have a whole support infrastructure of other specialized circuits. These circuits perform functions such as:
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Identifying each row and column (row address select and column address select)
Keeping track of the refresh sequence (counter)
Reading and restoring the signal from a cell (sense amplifier)
Telling a cell whether it should take a charge or not (write enable)
Other functions of the memory controller include a series of tasks that include identifying the type, speed and
amount of memory and checking for errors.
Static RAM works differently from DRAM. We'll look at how in the next section.
Static RAM
Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory
(see How Boolean Logic Works for details on flip-flops). A flip-flop for a memory cell takes four or six transistors
along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic
RAM. However, because it has more parts, a static memory cell takes up a lot more space on a chip than a
dynamic memory cell. Therefore, you get less memory per chip, and that makes static RAM a lot more
expensive.
Static RAM is fast and expensive, and dynamic RAM is less expensive and slower. So static RAM is used to
create the CPU's speed-sensitive cache, while dynamic RAM forms the larger system RAM space.
Memory chips in desktop computers originally used a pin configuration called dual inline package (DIP). This
pin configuration could be soldered into holes on the computer's motherboard or plugged into a socket that was
soldered on the motherboard. This method worked fine when computers typically operated on a couple of
megabytes or less of RAM, but as the need for memory grew, the number of chips needing space on the
motherboard increased.
The solution was to place the memory chips, along with all of the support components, on a separate printed
circuit board (PCB) that could then be plugged into a special connector (memory bank) on the motherboard.
Most of these chips use a small outline J-lead (SOJ) pin configuration, but quite a few manufacturers use the
24
thin small outline package (TSOP) configuration as well. The key difference between these newer pin types
and the original DIP configuration is that SOJ and TSOP chips are surface-mounted to the PCB. In other
words, the pins are soldered directly to the surface of the board, not inserted in holes or sockets.
Memory chips are normally only available as part of a card called a module. You've probably seen memory
listed as 8x32 or 4x16. These numbers represent the number of the chips multiplied by the capacity of each
individual chip, which is measured in megabits (Mb), or one million bits. Take the result and divide it by eight to
get the number of megabytes on that module. For example, 4x32 means that the module has four 32-megabit
chips. Multiply 4 by 32 and you get 128 megabits. Since we know that a byte has 8 bits, we need to divide our
result of 128 by 8. Our result is 16 megabytes!
Types of RAM
The type of board and connector used for RAM in desktop computers has evolved over the past few years. The
first types were proprietary, meaning that different computer manufacturers developed memory boards that
would only work with their specific systems. Then came SIMM, which stands for single in-line memory
module. This memory board used a 30-pin connector and was about 3.5 x .75 inches in size (about 9 x 2 cm).
In most computers, you had to install SIMMs in pairs of equal capacity and speed. This is because the width of
the bus is more than a single SIMM. For example, you would install two 8-megabyte (MB) SIMMs to get 16
megabytes total RAM. Each SIMM could send 8 bits of data at one time, while the system bus could handle 16
bits at a time. Later SIMM boards, slightly larger at 4.25 x 1 inch (about 11 x 2.5 cm), used a 72-pin connector
for increased bandwidth and allowed for up to 256 MB of RAM.
From the top: SIMM, DIMM and SODIMM memory modules
As processors grew in speed and bandwidth capability, the industry adopted a new standard in dual in-line
memory module (DIMM). With a whopping 168-pin or 184-pin connector and a size of 5.4 x 1 inch (about 14 x
2.5 cm), DIMMs range in capacity from 8 MB to 1 GB per module and can be installed singly instead of in pairs.
Most PC memory modules and the modules for the Mac G5 systems operate at 2.5 volts, while older Mac G4
systems typically use 3.3 volts. Another standard, Rambus in-line memory module (RIMM), is comparable in
size and pin configuration to DIMM but uses a special memory bus to greatly increase speed.
Many brands of notebook computers use proprietary memory modules, but several manufacturers use RAM
based on the small outline dual in-line memory module (SODIMM) configuration. SODIMM cards are small,
about 2 x 1 inch (5 x 2.5 cm), and have 144 or 200 pins. Capacity ranges from 16 MB to 1 GB per module. To
conserve space, the Apple iMac desktop computer uses SODIMMs instead of the traditional DIMMs. Subnotebook computers use even smaller DIMMs, known as MicroDIMMs, which have either 144 pins or 172 pins.
Most memory available today is highly reliable. Most systems simply have the memory controller check for
errors at start-up and rely on that. Memory chips with built-in error-checking typically use a method known as
parity to check for errors. Parity chips have an extra bit for every 8 bits of data. The way parity works is simple.
Let's look at even parity first.
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When the 8 bits in a byte receive data, the chip adds up the total number of 1s. If the total number of 1s is odd,
the parity bit is set to 1. If the total is even, the parity bit is set to 0. When the data is read back out of the bits,
the total is added up again and compared to the parity bit. If the total is odd and the parity bit is 1, then the data
is assumed to be valid and is sent to the CPU. But if the total is odd and the parity bit is 0, the chip knows that
there is an error somewhere in the 8 bits and dumps the data. Odd parity works the same way, but the parity
bit is set to 1 when the total number of 1s in the byte are even.
The problem with parity is that it discovers errors but does nothing to correct them. If a byte of data does not
match its parity bit, then the data are discarded and the system tries again. Computers in critical positions need
a higher level of fault tolerance. High-end servers often have a form of error-checking known as errorcorrection code (ECC). Like parity, ECC uses additional bits to monitor the data in each byte. The difference is
that ECC uses several bits for error checking -- how many depends on the width of the bus -- instead of one.
ECC memory uses a special algorithm not only to detect single bit errors, but actually correct them as well.
ECC memory will also detect instances when more than one bit of data in a byte fails. Such failures are very
rare, and they are not correctable, even with ECC.
The majority of computers sold today use nonparity memory chips. These chips do not provide any type of
built-in error checking, but instead rely on the memory controller for error detection.
The following are some common types of RAM:
 SRAM: Static random access memory uses multiple transistors, typically four to six, for each
memory cell but doesn't have a capacitor in each cell. It is used primarily for cache.
 DRAM: Dynamic random access memory has memory cells with a paired transistor and capacitor
requiring constant refreshing.
 FPM DRAM: Fast page mode dynamic random access memory was the original form of DRAM.







It waits through the entire process of locating a bit of data by column and row and then reading the
bit before it starts on the next bit. Maximum transfer rate to L2 cache is approximately 176 MBps.
EDO DRAM: Extended data-out dynamic random access memory does not wait for all of the
processing of the first bit before continuing to the next one. As soon as the address of the first bit
is located, EDO DRAM begins looking for the next bit. It is about five percent faster than FPM.
Maximum transfer rate to L2 cache is approximately 264 MBps.
SDRAM: Synchronous dynamic random access memory takes advantage of the burst mode
concept to greatly improve performance. It does this by staying on the row containing the
requested bit and moving rapidly through the columns, reading each bit as it goes. The idea is that
most of the time the data needed by the CPU will be in sequence. SDRAM is about five percent
faster than EDO RAM and is the most common form in desktops today. Maximum transfer rate to
L2 cache is approximately 528 MBps.
DDR SDRAM: Double data rate synchronous dynamic RAM is just like SDRAM except that is has
higher bandwidth, meaning greater speed. Maximum transfer rate to L2 cache is approximately
1,064 MBps (for DDR SDRAM 133 MHZ).
RDRAM: Rambus dynamic random access memory is a radical departure from the previous
DRAM architecture. Designed by Rambus, RDRAM uses a Rambus in-line memory module
(RIMM), which is similar in size and pin configuration to a standard DIMM. What makes RDRAM
so different is its use of a special high-speed data bus called the Rambus channel. RDRAM
memory chips work in parallel to achieve a data rate of 800 MHz, or 1,600 MBps. Since they
operate at such high speeds, they generate much more heat than other types of chips. To help
dissipate the excess heat Rambus chips are fitted with a heat spreader, which looks like a long
thin wafer. Just like there are smaller versions of DIMMs, there are also SO-RIMMs, designed for
notebook computers.
Credit Card Memory: Credit card memory is a proprietary self-contained DRAM memory module
that plugs into a special slot for use in notebook computers.
PCMCIA Memory Card: Another self-contained DRAM module for notebooks, cards of this type are
not proprietary and should work with any notebook computer whose system bus matches the
memory card's configuration.
CMOS RAM: CMOS RAM is a term for the small amount of memory used by your computer and
some other devices to remember things like hard disk settings -- see Why does my computer need
26
a battery? for details. This memory uses a small battery to provide it with the power it needs to
maintain the memory contents.
 VRAM: VideoRAM, also known as multiport dynamic random access memory (MPDRAM), is a
type of RAM used specifically for video adapters or 3-D accelerators. The "multiport" part comes
from the fact that VRAM normally has two independent access ports instead of one, allowing the
CPU and graphics processor to access the RAM simultaneously. VRAM is located on the graphics
card and comes in a variety of formats, many of which are proprietary. The amount of VRAM is a
determining factor in the resolution and color depth of the display. VRAM is also used to hold
graphics-specific information such as 3-D geometry data and texture maps. True multiport VRAM
tends to be expensive, so today, many graphics cards use SGRAM (synchronous graphics RAM)
instead. Performance is nearly the same, but SGRAM is cheaper.
For a comprehensive examination of RAM types, check out the Kingston Technology Ultimate Memory Guide.
How Much Do You Need?
It's been said that you can never have enough money, and the same holds true for RAM, especially if you do a
lot of graphics-intensive work or gaming. Next to the CPU itself, RAM is the most important factor in computer
performance. If you don't have enough, adding RAM can make more of a difference than getting a new CPU!
If your system responds slowly or accesses the hard drive constantly, then you need to add more RAM. If you
are running Windows XP, Microsoft recommends 128MB as the minimum RAM requirement. At 64MB, you may
experience frequent application problems. For optimal performance with standard desktop applications, 256MB
is recommended. If you are running Windows 95/98, you need a bare minimum of 32 MB, and your computer
will work much better with 64 MB. Windows NT/2000 needs at least 64 MB, and it will take everything you can
throw at it, so you'll probably want 128 MB or more.
Linux works happily on a system with only 4 MB of RAM. If you plan to add X-Windows or do much serious
work, however, you'll probably want 64 MB. Mac OS X systems should have a minimum of 128 MB, or for
optimal performance, 512 MB.
The amount of RAM listed for each system above is estimated for normal usage -- accessing the Internet, word
processing, standard home/office applications and light entertainment. If you do computer-aided design (CAD),
3-D modeling/animation or heavy data processing, or if you are a serious gamer, then you will most likely need
more RAM. You may also need more RAM if your computer acts as a server of some sort (Web pages,
database, application, FTP or network).
Another question is how much VRAM you want on your video card. Almost all cards that you can buy today
have at least 16 MB of RAM. This is normally enough to operate in a typical office environment. You should
probably invest in a 32-MB or better graphics card if you want to do any of the following:
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


Play realistic games
Capture and edit video
Create 3-D graphics
Work in a high-resolution, full-color environment
Design full-color illustrations
When shopping for video cards, remember that your monitor and computer must be capable of supporting the
card you choose.
Memory Upgrade Center
Click on a sub-category to show products in that sub-category.
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How to Install RAM
Most of the time, installing RAM is a very simple and straightforward procedure. The key is to do your research.
Here's what you need to know:
 How much RAM you have
 How much RAM you wish to add
 Form factor
 RAM type
 Tools needed
 Warranty
 Where it goes
RAM is usually sold in multiples of 16 megabytes: 16, 32, 64, 128, 256, 512, 1024 (which is the same as 1GB).
This means that if you currently have a system with 64 MB RAM and you want at least 100 MB RAM total, then
you will probably need to add another 64 MB module.
Once you know how much RAM you want, check to see what form factor (card type) you need to buy. You can
find this in the manual that came with your computer, or you can contact the manufacturer. An important thing
to realize is that your options will depend on the design of your computer. Most computers sold today for normal
home/office use have DIMM slots. High-end systems are moving to RIMM technology, which will eventually
take over in standard desktop computers as well. Since DIMM and RIMM slots look a lot alike, be very careful
to make sure you know which type your computer uses. Putting the wrong type of card in a slot can cause
damage to your system and ruin the card.
You will also need to know what type of RAM is required. Some computers require very specific types of RAM
to operate. For example, your computer may only work with 60ns-70ns parity EDO RAM. Most computers are
not quite that restrictive, but they do have limitations. For optimal performance, the RAM you add to your
computer must also match the existing RAM in speed, parity and type. The most common type available today
is SDRAM.
Additionally, some computers support Dual Channel RAM configuration either as an option or as a requirement.
Dual Channel means that RAM modules are installed in matched pairs, so if there is a 512MB RAM card
installed, there is another 512 MB card installed next to it. When Dual Channel is an optional configuration,
installing RAM in matched pairs speeds up the performance of certain applications. When it's a requirement, as
in computers with the Mac G5 chip(s), the computer will not function properly without matched pairs of RAM
chips.
For complete guidelines on setting up Dual Channel configuration on Intel Pentium 4-based systems, check out
this guide.
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Before you open your computer, check to make sure you won't be voiding the warranty. Some manufacturers
seal the case and request that the customer have an authorized technician install RAM. If you're set to open the
case, turn off and unplug the computer. Ground yourself by using an anti-static pad or wrist strap to discharge
any static electricity. Depending on your computer, you may need a screwdriver or nut-driver to open the case.
Many systems sold today come in tool-less cases that use thumbscrews or a simple latch.
To install more RAM, look for memory modules on your computer's
motherboard. At the left is a Macintosh G4 and on the right is a PC.
The actual installation of the memory module does not normally require any tools. RAM is installed in a series
of slots on the motherboard known as the memory bank. The memory module is notched at one end so you
won't be able to insert it in the wrong direction. For SIMMs and some DIMMs, you install the module by placing
it in the slot at approximately a 45-degree angle. Then push it forward until it is perpendicular to the
motherboard and the small metal clips at each end snap into place. If the clips do not catch properly, check to
make sure the notch is at the right end and the card is firmly seated. Many DIMMs do not have metal clips; they
rely on friction to hold them in place. Again, just make sure the module is firmly seated in the slot.
Once the module is installed, close the case, plug the computer back in and power it up. When the computer
starts the POST, it should automatically recognize the memory. That's all there is to it!
For more information on RAM, other types of computer memory and related topics, check out the links on the
next page.
How BIOS Works
One of the most common uses of Flash memory is for the basic input/output system of your computer,
commonly known as the BIOS (pronounced "bye-ose"). On virtually every computer available, the BIOS makes
sure all the other chips, hard drives, ports and CPU function together.
Every desktop and laptop computer in common use today contains a microprocessor as its central processing
unit. The microprocessor is the hardware component. To get its work done, the microprocessor executes a set
of instructions known as software (see How Microprocessors Work for details). You are probably very familiar
with two different types of software:
 The operating system - The operating system provides a set of services for the applications
running on your computer, and it also provides the fundamental user interface for your computer.
Windows 98 and Linux are examples of operating systems. (See How Operating Systems Work for
lots of details.)
 The applications - Applications are pieces of software that are programmed to perform specific
tasks. On your computer right now you probably have a browser application, a word processing
application, an e-mail application and so on. You can also buy new applications and install them.
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It turns out that the BIOS is the third type of software your computer needs to operate successfully. In this
article, you'll learn all about BIOS -- what it does, how to configure it and what to do if your BIOS needs
updating.
What BIOS Does
The BIOS software has a number of different roles, but its most important role is to load the operating system.
When you turn on your computer and the microprocessor tries to execute its first instruction, it has to get that
instruction from somewhere. It cannot get it from the operating system because the operating system is located
on a hard disk, and the microprocessor cannot get to it without some instructions that tell it how. The BIOS
provides those instructions. Some of the other common tasks that the BIOS performs include:
 A power-on self-test (POST) for all of the different hardware components in the system to make sure
everything is working properly
 Activating other BIOS chips on different cards installed in the computer - For example, SCSI and
graphics cards often have their own BIOS chips.
 Providing a set of low-level routines that the operating system uses to interface to different hardware
devices - It is these routines that give the BIOS its name. They manage things like the keyboard,
the screen, and the serial and parallel ports, especially when the computer is booting.
 Managing a collection of settings for the hard disks, clock, etc.
The BIOS is special software that interfaces the major hardware components of your computer with the
operating system. It is usually stored on a Flash memory chip on the motherboard, but sometimes the chip is
another type of ROM.
BIOS uses Flash memory, a type of ROM.
When you turn on your computer, the BIOS does several things. This is its usual sequence:
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Check the CMOS Setup for custom settings
Load the interrupt handlers and device drivers
Initialize registers and power management
Perform the power-on self-test (POST)
Display system settings
Determine which devices are bootable
Initiate the bootstrap sequence
The first thing the BIOS does is check the information stored in a tiny (64 bytes) amount of RAM located on a
complementary metal oxide semiconductor (CMOS) chip. The CMOS Setup provides detailed information
particular to your system and can be altered as your system changes. The BIOS uses this information to modify
or supplement its default programming as needed. We will talk more about these settings later.
Interrupt handlers are small pieces of software that act as translators between the hardware components and
the operating system. For example, when you press a key on your keyboard, the signal is sent to the keyboard
interrupt handler, which tells the CPU what it is and passes it on to the operating system. The device drivers
are other pieces of software that identify the base hardware components such as keyboard, mouse, hard drive
and floppy drive. Since the BIOS is constantly intercepting signals to and from the hardware, it is usually
copied, or shadowed, into RAM to run faster.
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Booting the Computer
Whenever you turn on your computer, the first thing you see is the BIOS software doing its thing. On many
machines, the BIOS displays text describing things like the amount of memory installed in your computer, the
type of hard disk and so on. It turns out that, during this boot sequence, the BIOS is doing a remarkable amount
of work to get your computer ready to run. This section briefly describes some of those activities for a typical
PC.
After checking the CMOS Setup and loading the interrupt handlers, the BIOS determines whether the video
card is operational. Most video cards have a miniature BIOS of their own that initializes the memory and
graphics processor on the card. If they do not, there is usually video driver information on another ROM on the
motherboard that the BIOS can load.
Next, the BIOS checks to see if this is a cold boot or a reboot. It does this by checking the value at memory
address 0000:0472. A value of 1234h indicates a reboot, and the BIOS skips the rest of POST. Anything else is
considered a cold boot.
If it is a cold boot, the BIOS verifies RAM by performing a read/write test of each memory address. It checks the
PS/2 ports or USB ports for a keyboard and a mouse. It looks for a peripheral component interconnect (PCI)
bus and, if it finds one, checks all the PCI cards. If the BIOS finds any errors during the POST, it will notify you
by a series of beeps or a text message displayed on the screen. An error at this point is almost always a
hardware problem.
The BIOS then displays some details about your system. This typically includes information about:
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The processor
The floppy drive and hard drive
Memory
BIOS revision and date
Display
Any special drivers, such as the ones for small computer system interface (SCSI) adapters, are loaded from
the adapter, and the BIOS displays the information. The BIOS then looks at the sequence of storage devices
identified as boot devices in the CMOS Setup. "Boot" is short for "bootstrap," as in the old phrase, "Lift yourself
up by your bootstraps." Boot refers to the process of launching the operating system. The BIOS will try to
initiate the boot sequence from the first device. If the BIOS does not find a device, it will try the next device in
the list. If it does not find the proper files on a device, the startup process will halt. If you have ever left a floppy
disk in the drive when you restarted your computer, you have probably seen this message.
This is the message you get if a floppy disk is in the drive
when you restart your computer.
The BIOS has tried to boot the computer off of the floppy disk left in the drive. Since it did not find the correct
system files, it could not continue. Of course, this is an easy fix. Simply pop out the disk and press a key to
continue.
Configuring BIOS
In the previous list, you saw that the BIOS checks the CMOS Setup for custom settings. Here's what you do to
change those settings.
To enter the CMOS Setup, you must press a certain key or combination of keys during the initial startup
sequence. Most systems use "Esc," "Del," "F1," "F2," "Ctrl-Esc" or "Ctrl-Alt-Esc" to enter setup. There is
usually a line of text at the bottom of the display that tells you "Press ___ to Enter Setup."
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Once you have entered setup, you will see a set of text screens with a number of options. Some of these are
standard, while others vary according to the BIOS manufacturer. Common options include:
 System Time/Date - Set the system time and date
 Boot Sequence - The order that BIOS will try to load the operating system
 Plug and Play - A standard for auto-detecting connected devices; should be set to "Yes" if your
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computer and operating system both support it
Mouse/Keyboard - "Enable Num Lock," "Enable the Keyboard," "Auto-Detect Mouse"...
Drive Configuration - Configure hard drives, CD-ROM and floppy drives
Memory - Direct the BIOS to shadow to a specific memory address
Security - Set a password for accessing the computer
Power Management - Select whether to use power management, as well as set the amount of time
for standby and suspend
Exit - Save your changes, discard your changes or restore default settings
CMOS Setup
Be very careful when making changes to setup. Incorrect settings may keep your computer from booting. When
you are finished with your changes, you should choose "Save Changes" and exit. The BIOS will then restart
your computer so that the new settings take effect.
The BIOS uses CMOS technology to save any changes made to the computer's settings. With this technology,
a small lithium or Ni-Cad battery can supply enough power to keep the data for years. In fact, some of the
newer chips have a 10-year, tiny lithium battery built right into the CMOS chip!
Updating Your BIOS
Occasionally, a computer will need to have its BIOS updated. This is especially true of older machines. As new
devices and standards arise, the BIOS needs to change in order to understand the new hardware. Since the
BIOS is stored in some form of ROM, changing it is a bit harder than upgrading most other types of software.
To change the BIOS itself, you'll probably need a special program from the computer or BIOS manufacturer.
Look at the BIOS revision and date information displayed on system startup or check with your computer
manufacturer to find out what type of BIOS you have. Then go to the BIOS manufacturer's Web site to see if an
upgrade is available. Download the upgrade and the utility program needed to install it. Sometimes the utility
and update are combined in a single file to download. Copy the program, along with the BIOS update, onto a
floppy disk. Restart your computer with the floppy disk in the drive, and the program erases the old BIOS and
writes the new one. You can find a BIOS Wizard that will check your BIOS at BIOS Upgrades.
Major BIOS manufacturers include:
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American Megatrends Inc. (AMI)
Phoenix Technologies
ALi
Winbond
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As with changes to the CMOS Setup, be careful when upgrading your BIOS. Make sure you are upgrading to a
version that is compatible with your computer system. Otherwise, you could corrupt the BIOS, which means you
won't be able to boot your computer. If in doubt, check with your computer manufacturer to be sure you need to
upgrade.
For more information on BIOS and related topics, check out the links on the next page.
How Operating Systems Work
If you have a computer, then you have heard about operating systems. Any desktop or laptop PC that you buy
normally comes pre-loaded with Windows XP. Macintosh computers come pre-loaded with OS X. Many
corporate servers use the Linux or UNIX operating systems. The operating system (OS) is the first thing loaded
onto the computer -- without the operating system, a computer is useless.
More recently, operating systems have started to pop up in smaller computers as well. If you like to tinker with
electronic devices, you are probably pleased that operating systems can now be found on many of the devices
we use every day, from cell phones to wireless access points. The computers used in these little devices have
gotten so powerful that they can now actually run an operating system and applications. The computer in a
typical modern cell phone is now more powerful than a desktop computer from 20 years ago, so this
progression makes sense and is a natural development. In any device that has an operating system, there's
usually a way to make changes to how the device works. This is far from a happy accident; one of the reasons
operating systems are made out of portable code rather than permanent physical circuits is so that they can be
changed or modified without having to scrap the whole device.
Box shot reprinted with permission from Microsoft Corporation
©2003 Microsoft Corporation. All rights reserved.
Microsoft XP operating system
For a desktop computer user, this means you can add a new security update, system patch, new application or
often even a new operating system entirely rather than junk your computer and start again with a new one
when you need to make a change. As long as you understand how an operating system works and know how
to get at it, you can in many cases change some of the ways it behaves. And, it's as true of your cell phone as it
is of your computer.
The purpose of an operating system is to organize and control hardware and software so that the device it lives
in behaves in a flexible but predictable way. In this article, we'll tell you what a piece of software must do to be
called an operating system, show you how the operating system in your desktop computer works and give you
some examples of how to take control of the other operating systems around you.
The Bare Bones
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Not all computers have operating systems. The computer that controls the
microwave oven in your kitchen, for example, doesn't need an operating
system. It has one set of tasks to perform, very straightforward input to
expect (a numbered keypad and a few pre-set buttons) and simple, neverchanging hardware to control. For a computer like this, an operating system
would be unnecessary baggage, driving up the development and
manufacturing costs significantly and adding complexity where none is
required. Instead, the computer in a microwave oven simply runs a single
hard-wired program all the time.
For other devices, an operating system creates the ability to:
 serve a variety of purposes
 interact with users in more complicated ways
 keep up with needs that change over time
All desktop computers have operating systems. The most common are the Windows family of operating
systems developed by Microsoft, the Macintosh operating systems developed by Apple and the UNIX family of
operating systems (which have been developed by a whole history of individuals, corporations and
collaborators). There are hundreds of other operating systems available for special-purpose applications,
including specializations for mainframes, robotics, manufacturing, real-time control systems and so on.
What Does It Do?
At the simplest level, an operating system does two things:
 It manages the hardware and software resources of the system. In a desktop computer, these
resources include such things as the processor, memory, disk space, etc. (On a cell phone, they
include the keypad, the screen, the address book, the phone dialer, the battery and the network
connection.)
 It provides a stable, consistent way for applications to deal with the hardware without having to
know all the details of the hardware.
The first task, managing the hardware and software resources, is very important, as various programs and input
methods compete for the attention of the central processing unit (CPU) and demand memory, storage and
input/output (I/O) bandwidth for their own purposes. In this capacity, the operating system plays the role of the
good parent, making sure that each application gets the necessary resources while playing nicely with all the
other applications, as well as husbanding the limited capacity of the system to the greatest good of all the users
and applications.
The second task, providing a consistent application interface, is especially important if there is to be more than
one of a particular type of computer using the operating system, or if the hardware making up the computer is
ever open to change. A consistent application program interface (API) allows a software developer to write
an application on one computer and have a high level of confidence that it will run on another computer of the
same type, even if the amount of memory or the quantity of storage is different on the two machines.
Even if a particular computer is unique, an operating system can ensure that applications continue to run when
hardware upgrades and updates occur. This is because the operating system and not the application is
charged with managing the hardware and the distribution of its resources. One of the challenges facing
developers is keeping their operating systems flexible enough to run hardware from the thousands of vendors
manufacturing computer equipment. Today's systems can accommodate thousands of different printers, disk
drives and special peripherals in any possible combination.
What Kinds Are There?
Within the broad family of operating systems, there are generally four types, categorized based on the types of
computers they control and the sort of applications they support. The broad categories are:
 Real-time operating system (RTOS) - Real-time operating systems are used to control machinery,
scientific instruments and industrial systems. An RTOS typically has very little user-interface
capability, and no end-user utilities, since the system will be a "sealed box" when delivered for
use. A very important part of an RTOS is managing the resources of the computer so that a
34
particular operation executes in precisely the same amount of time every time it occurs. In a
complex machine, having a part move more quickly just because system resources are available
may be just as catastrophic as having it not move at all because the system is busy.
 Single-user, single task - As the name implies, this operating system is designed to manage the
computer so that one user can effectively do one thing at a time. The Palm OS for Palm handheld
computers is a good example of a modern single-user, single-task operating system.
 Single-user, multi-tasking - This is the type of operating system most people use on their desktop
and laptop computers today. Microsoft's Windows and Apple's MacOS platforms are both
examples of operating systems that will let a single user have several programs in operation at the
same time. For example, it's entirely possible for a Windows user to be writing a note in a word
processor while downloading a file from the Internet while printing the text of an e-mail message.
 Multi-user - A multi-user operating system allows many different users to take advantage of the
computer's resources simultaneously. The operating system must make sure that the
requirements of the various users are balanced, and that each of the programs they are using has
sufficient and separate resources so that a problem with one user doesn't affect the entire
community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of
multi-user operating systems.
Photo courtesy Apple
Mac OS X Panther screen shot
It's important to differentiate here between multi-user operating systems and single-user operating systems that
support networking. Windows 2000 and Novell Netware can each support hundreds or thousands of networked
users, but the operating systems themselves aren't true multi-user operating systems. The system
administrator is the only "user" for Windows 2000 or Netware. The network support and all of the remote user
logins the network enables are, in the overall plan of the operating system, a program being run by the
administrative user.
With the different types of operating systems in mind, it's time to look at the
Wake-Up Call
When you turn on the power to a computer, the first program that runs is usually a set of instructions kept in the
computer's read-only memory (ROM). This code examines the system hardware to make sure everything is
functioning properly. This power-on self test (POST) checks the CPU, memory, and basic input-output
systems (BIOS) for errors and stores the result in a special memory location. Once the POST has successfully
completed, the software loaded in ROM (sometimes called the BIOS or firmware) will begin to activate the
computer's disk drives. In most modern computers, when the computer activates the hard disk drive, it finds the
first piece of the operating system: the bootstrap loader.
The bootstrap loader is a small program that has a single function: It loads the operating system into memory
and allows it to begin operation. In the most basic form, the bootstrap loader sets up the small driver programs
that interface with and control the various hardware subsystems of the computer. It sets up the divisions of
memory that hold the operating system, user information and applications. It establishes the data structures
that will hold the myriad signals, flags and semaphores that are used to communicate within and between the
35
subsystems and applications of the computer. Then it turns control of the computer over to the operating
system.
The operating system's tasks, in the most general sense, fall into six categories:
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Processor management
Memory management
Device management
Storage management
Application interface
User interface
While there are some who argue that an operating system should do more than these six tasks, and some
operating-system vendors do build many more utility programs and auxiliary functions into their operating
systems, these six tasks define the core of nearly all operating systems. Let's look at the tools the operating
system uses to perform each of these functions.
Processor Management
The heart of managing the processor comes down to two related issues:
 Ensuring that each process and application receives enough of the processor's time to function
properly.
 Using as many processor cycles for real work as is possible.
The basic unit of software that the operating system deals with in scheduling the work done by the processor is
either a process or a thread, depending on the operating system.
It's tempting to think of a process as an application, but that gives an incomplete picture of how processes
relate to the operating system and hardware. The application you see (word processor or spreadsheet or game)
is, indeed, a process, but that application may cause several other processes to begin, for tasks like
communications with other devices or other computers. There are also numerous processes that run without
giving you direct evidence that they ever exist. For example, Windows XP and UNIX can have dozens of
background processes running to handle the network, memory management, disk management, virus checking
and so on.
A process, then, is software that performs some action and can be controlled -- by a user, by other applications
or by the operating system.
It is processes, rather than applications, that the operating system controls and schedules for execution by the
CPU. In a single-tasking system, the schedule is straightforward. The operating system allows the application to
begin running, suspending the execution only long enough to deal with interrupts and user input.
Interrupts are special signals sent by hardware or software to the CPU. It's as if some part of the computer
suddenly raised its hand to ask for the CPU's attention in a lively meeting. Sometimes the operating system will
schedule the priority of processes so that interrupts are masked -- that is, the operating system will ignore the
interrupts from some sources so that a particular job can be finished as quickly as possible. There are some
interrupts (such as those from error conditions or problems with memory) that are so important that they can't
be ignored. These non-maskable interrupts (NMIs) must be dealt with immediately, regardless of the other
tasks at hand.
While interrupts add some complication to the execution of processes in a single-tasking system, the job of the
operating system becomes much more complicated in a multi-tasking system. Now, the operating system must
arrange the execution of applications so that you believe that there are several things happening at once. This
is complicated because the CPU can only do one thing at a time. In order to give the appearance of lots of
things happening at the same time, the operating system has to switch between different processes thousands
of times a second. Here's how it happens:
 A process occupies a certain amount of RAM. It also makes use of registers, stacks and queues
within the CPU and operating-system memory space.
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 When two processes are multi-tasking, the operating system allots a certain number of CPU
execution cycles to one program.
 After that number of cycles, the operating system makes copies of all the registers, stacks and
queues used by the processes, and notes the point at which the process paused in its execution.
 It then loads all the registers, stacks and queues used by the second process and allows it a certain
number of CPU cycles.
 When those are complete, it makes copies of all the registers, stacks and queues used by the
second program, and loads the first program.
All of the information needed to keep track of a process when switching is kept in a data package called a
process control block. The process control block typically contains:
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An ID number that identifies the process
Pointers to the locations in the program and its data where processing last occurred
Register contents
States of various flags and switches
Pointers to the upper and lower bounds of the memory required for the process
A list of files opened by the process
The priority of the process
The status of all I/O devices needed by the process
Each process has a status associated with it. Many processes consume no CPU time until they get some sort
of input. For example, a process might be waiting on a keystroke from the user. While it is waiting for the
keystroke, it uses no CPU time. While it is waiting, it is "suspended". When the keystroke arrives, the OS
changes its status. When the status of the process changes, from pending to active, for example, or from
suspended to running, the information in the process control block must be used like the data in any other
program to direct execution of the task-switching portion of the operating system.
This process swapping happens without direct user interference, and each process gets enough CPU cycles to
accomplish its task in a reasonable amount of time. Trouble can come, though, if the user tries to have too
many processes functioning at the same time. The operating system itself requires some CPU cycles to
perform the saving and swapping of all the registers, queues and stacks of the application processes. If enough
processes are started, and if the operating system hasn't been carefully designed, the system can begin to use
the vast majority of its available CPU cycles to swap between processes rather than run processes. When this
happens, it's called thrashing, and it usually requires some sort of direct user intervention to stop processes
and bring order back to the system.
One way that operating-system designers reduce the chance of thrashing is by reducing the need for new
processes to perform various tasks. Some operating systems allow for a "process-lite," called a thread, that
can deal with all the CPU-intensive work of a normal process, but generally does not deal with the various types
of I/O and does not establish structures requiring the extensive process control block of a regular process. A
process may start many threads or other processes, but a thread cannot start a process.
So far, all the scheduling we've discussed has concerned a single CPU. In a system with two or more CPUs,
the operating system must divide the workload among the CPUs, trying to balance the demands of the required
processes with the available cycles on the different CPUs. Asymmetric operating systems use one CPU for
their own needs and divide application processes among the remaining CPUs. Symmetric operating systems
divide themselves among the various CPUs, balancing demand versus CPU availability even when the
operating system itself is all that's running.
Even if the operating system is the only software with execution needs, the CPU is not the only resource to be
scheduled. Memory management is the next crucial step in making sure that all processes run smoothly.
Memory Storage and Management
When an operating system manages the computer's memory, there are two broad tasks to be accomplished:
 Each process must have enough memory in which to execute, and it can neither run into the
memory space of another process nor be run into by another process.
 The different types of memory in the system must be used properly so that each process can run
most effectively.
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The first task requires the operating system to set up memory boundaries for types of software and for
individual applications.
As an example, let's look at an imaginary small system with 1 megabyte (1,000 kilobytes) of RAM. During the
boot process, the operating system of our imaginary computer is designed to go to the top of available memory
and then "back up" far enough to meet the needs of the operating system itself. Let's say that the operating
system needs 300 kilobytes to run. Now, the operating system goes to the bottom of the pool of RAM and starts
building up with the various driver software required to control the hardware subsystems of the computer. In our
imaginary computer, the drivers take up 200 kilobytes. So after getting the operating system completely loaded,
there are 500 kilobytes remaining for application processes.
When applications begin to be loaded into memory, they are loaded in block sizes determined by the operating
system. If the block size is 2 kilobytes, then every process that is loaded will be given a chunk of memory that is
a multiple of 2 kilobytes in size. Applications will be loaded in these fixed block sizes, with the blocks starting
and ending on boundaries established by words of 4 or 8 bytes. These blocks and boundaries help to ensure
that applications won't be loaded on top of one another's space by a poorly calculated bit or two. With that
ensured, the larger question is what to do when the 500-kilobyte application space is filled.
In most computers, it's possible to add memory beyond the original capacity. For example, you might expand
RAM from 1 to 2 megabytes. This works fine, but tends to be relatively expensive. It also ignores a fundamental
fact of computing -- most of the information that an application stores in memory is not being used at any given
moment. A processor can only access memory one location at a time, so the vast majority of RAM is unused at
any moment. Since disk space is cheap compared to RAM, then moving information in RAM to hard disk can
greatly expand RAM space at no cost. This technique is called virtual memory management.
Disk storage is only one of the memory types that must be managed by the operating system, and is the
slowest. Ranked in order of speed, the types of memory in a computer system are:
 High-speed cache - This is fast, relatively small amounts of memory that are available to the CPU
through the fastest connections. Cache controllers predict which pieces of data the CPU will need
next and pull it from main memory into high-speed cache to speed up system performance.
 Main memory - This is the RAM that you see measured in megabytes when you buy a computer.
 Secondary memory - This is most often some sort of rotating magnetic storage that keeps
applications and data available to be used, and serves as virtual RAM under the control of the
operating system.
The operating system must balance the needs of the various processes with the availability of the different
types of memory, moving data in blocks (called pages) between available memory as the schedule of
processes dictates.
Device Management
The path between the operating system and virtually all hardware not on the computer's motherboard goes
through a special program called a driver. Much of a driver's function is to be the translator between the
electrical signals of the hardware subsystems and the high-level programming languages of the operating
system and application programs. Drivers take data that the operating system has defined as a file and
translate them into streams of bits placed in specific locations on storage devices, or a series of laser pulses in
a printer.
Because there are such wide differences in the hardware controlled through drivers, there are differences in the
way that the driver programs function, but most are run when the device is required, and function much the
same as any other process. The operating system will frequently assign high-priority blocks to drivers so that
the hardware resource can be released and readied for further use as quickly as possible.
One reason that drivers are separate from the operating system is so that new functions can be added to the
driver -- and thus to the hardware subsystems -- without requiring the operating system itself to be modified,
recompiled and redistributed. Through the development of new hardware device drivers, development often
performed or paid for by the manufacturer of the subsystems rather than the publisher of the operating system,
input/output capabilities of the overall system can be greatly enhanced.
38
Managing input and output is largely a matter of managing queues and buffers, special storage facilities that
take a stream of bits from a device, perhaps a keyboard or a serial port, hold those bits, and release them to
the CPU at a rate slow enough for the CPU to cope with. This function is especially important when a number of
processes are running and taking up processor time. The operating system will instruct a buffer to continue
taking input from the device, but to stop sending data to the CPU while the process using the input is
suspended. Then, when the process needing input is made active once again, the operating system will
command the buffer to send data. This process allows a keyboard or a modem to deal with external users or
computers at a high speed even though there are times when the CPU can't use input from those sources.
Managing all the resources of the computer system is a large part of the operating system's function and, in the
case of real-time operating systems, may be virtually all the functionality required. For other operating systems,
though, providing a relatively simple, consistent way for applications and humans to use the power of the
hardware is a crucial part of their reason for existing.
Interface to the World
Application Interface
Just as drivers provide a way for applications to make use of hardware subsystems without having to know
every detail of the hardware's operation, application program interfaces (APIs) let application programmers
use functions of the computer and operating system without having to directly keep track of all the details in the
CPU's operation. Let's look at the example of creating a hard disk file for holding data to see why this can be
important.
A programmer writing an application to record data from a scientific instrument might want to allow the scientist
to specify the name of the file created. The operating system might provide an API function named MakeFile
for creating files. When writing the program, the programmer would insert a line that looks like this:
MakeFile [1, %Name, 2]
In this example, the instruction tells the operating system to create a file that will allow random access to its
data (signified by the 1 -- the other option might be 0 for a serial file), will have a name typed in by the user
(%Name) and will be a size that varies depending on how much data is stored in the file (signified by the 2 -other options might be zero for a fixed size, and 1 for a file that grows as data is added but does not shrink
when data is removed). Now, let's look at what the operating system does to turn the instruction into action.
The operating system sends a query to the disk drive to get the location of the first available free storage
location.
With that information, the operating system creates an entry in the file system showing the beginning and
ending locations of the file, the name of the file, the file type, whether the file has been archived, which users
have permission to look at or modify the file, and the date and time of the file's creation.
The operating system writes information at the beginning of the file that identifies the file, sets up the type of
access possible and includes other information that ties the file to the application. In all of this information, the
queries to the disk drive and addresses of the beginning and ending point of the file are in formats heavily
dependent on the manufacturer and model of the disk drive.
Because the programmer has written the program to use the API for disk storage, the programmer doesn't have
to keep up with the instruction codes, data types and response codes for every possible hard disk and tape
drive. The operating system, connected to drivers for the various hardware subsystems, deals with the
changing details of the hardware -- the programmer must simply write code for the API and trust the operating
system to do the rest.
APIs have become one of the most hotly contested areas of the computer industry in recent years. Companies
realize that programmers using their API will ultimately translate this into the ability to control and profit from a
particular part of the industry. This is one of the reasons that so many companies have been willing to provide
applications like readers or viewers to the public at no charge. They know consumers will request that programs
take advantage of the free readers, and application companies will be ready to pay royalties to allow their
software to provide the functions requested by the consumers.
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User Interface
Just as the API provides a consistent way for applications to use the resources of the computer system, a user
interface (UI) brings structure to the interaction between a user and the computer. In the last decade, almost all
development in user interfaces has been in the area of the graphical user interface (GUI), with two models,
Apple's Macintosh and Microsoft's Windows, receiving most of the attention and gaining most of the market
share. The popular, open-source Linux operating system also supports a graphical user interface.
Screen shot copyright © 2003 Red Hat, Inc. All rights reserved.
Reprinted with permission from Red Hat, Inc.
Screen shot of Red Hat's Linux operating system
There are other user interfaces, some graphical and some not, for other operating systems.
Unix, for example, has user interfaces called shells that present a user interface more flexible and powerful
than the standard operating system text-based interface. Programs such as the Korn Shell and the C Shell are
text-based interfaces that add important utilities, but their main purpose is to make it easier for the user to
manipulate the functions of the operating system. There are also graphical user interfaces, such as X-Windows
and Gnome, that make Unix and Linux more like Windows and Macintosh computers from the user's point of
view.
It's important to remember that in all of these examples, the user interface is a program or set of programs that
sits as a layer above the operating system itself. The same thing is true, with somewhat different mechanisms,
of both Windows and Macintosh operating systems. The core operating-system functions -- the management of
the computer system -- lie in the kernel of the operating system. The display manager is separate, though it
may be tied tightly to the kernel beneath. The ties between the operating-system kernel and the user interface,
utilities and other software define many of the differences in operating systems today, and will further define
them in the future.
What's New
The Growing Importance of Networks
For desktop systems, access to a LAN or the Internet has become such an expected feature that in many ways
it's hard to discuss an operating system without making reference to its connections to other computers and
servers. Operating system developers have made the Internet the standard method for delivering crucial
operating system updates and bug fixes. Although it is possible to receive these updates via CD, it is becoming
increasingly less common. In fact, some entire operating systems themselves are only available through
distribution over the Internet.
Further, a process called NetBooting has streamlined the capability to move the working operating system of a
standard consumer desktop computer - kernel, user interface and all - off of the machine it controls. This was
previously only possible for experienced power-users on multi-user platforms like UNIX and with a suite of
specialized applications. NetBooting allows the operating system for one computer to be served over a network
connection, by a remote computer connected anywhere in the network. One NetBoot server can serve
operating systems to several dozen client computers simultaneously, and to the user sitting in front of each
40
client computer the experience is just like they are using their familiar desktop operating system like Windows
or MacOS.
Open Source
One question concerning the future of operating systems revolves around the ability of a particular philosophy
of software distribution to create an operating system useable by corporations
and consumers together.
Linux, the operating system created and distributed according to the principles
of open source, has had a significant impact on the operating system in
general. Most operating systems, drivers and utility programs are written by
commercial organizations that distribute executable versions of their software
-- versions that can't be studied or altered. Open source requires the
distribution of original source materials that can be studied, altered and built
upon, with the results once again freely distributed. In the desktop computer
realm, this has led to the development and distribution of countless useful and
cost-free applications like the image manipulation program GIMP and the
popular web server Apache. In the consumer device realm, the use of Linux
has paved the way for individual users to have greater control over how their
devices behave.
Logo courtesy Larry Ewing
Linux logo
Getting at the OS
Many consumer devices like cell phones and routers deliberately hide access to the operating system from the
user, mostly to make sure that it's not inadvertently broken or removed. In many cases, they leave open a
"developer's mode" or "programmer's mode" which allow changes to be made if you know how to find it. Often
these systems may be programmed in such a way that there are only a limited range of changes that can be
made. But some devices leave open both a mode of access and the means of making powerful changes,
especially those that use Linux. Here are a couple of examples:
 The TiVo DVR runs on a modified version of Linux. All of the modifications are public knowledge,
and can be downloaded here along with some special tools for manipulating the code. Many
enterprising TiVo users have done just that, adding functionality to their systems, from increasing
the storage capacity to getting to UNIX shells to changing the mode from NTSC to PAL. Here's a
FAQ on how to hack your TiVo.
Photo courtesy Amazon.com
Philips HDR312 TiVo 30-Hour Digital Video Recorder and
Linksys EZXS55W EtherFast 10/100 5-Port Workgroup Switch
 Many home routers also run on Linux, including those made by Linksys. This article from G4TechTV
discusses how to hack your Linksys Router and take control of the Linux inside.
For more information on operating systems and related topics, check out the links on the next page.
Defining a PC
Here is one way to think about it: A PC is a general-purpose information processing device. It can take information
from a person (through the keyboard and mouse), from a device (like a floppy disk or CD) or from the network
(through a modem or a network card) and process it. Once processed, the information is shown to the user (on the
monitor), stored on a device (like a hard disk) or sent somewhere else on the network (back through the modem or
network card).
We have lots of special-purpose processors in our lives. An MP3 player is a specialized computer for
processing MP3 files. A GPS is a specialized computer for handling GPS signals. A Nintendo DS is a
41
specialized computer for handling games, but it can't do anything else. A PC can do it all because it is generalpurpose.
PC Connections
A typical computer connects to the world around it in three different ways: input/output devices, ports and
networking.
Input/Output
No matter how powerful the components inside your computer are, you need a way to interact with them. This
interaction is called input/output (I/O). The most common types of I/O in PCs are:




Monitor - The monitor is the primary device for displaying information from the computer.
Keyboard - The keyboard is the primary device for entering information into the computer.
Mouse - The mouse is the primary device for navigating and interacting with the computer
Removable storage - Removable storage devices allow you to add new information to your
computer very easily, as well as save information that you want to carry to a different location.
 Floppy disk - The most common form of removable storage, floppy disks are
extremely inexpensive and easy to save information to.
 CD-ROM - CD-ROM (compact disc, read-only memory) is a popular form of
distribution of commercial software. Many systems now offer CD-R (recordable) and
CD-RW (rewritable), which can also record.
 Flash memory - Based on a type of ROM called electrically erasable
programmable read-only memory (EEPROM), Flash memory provides fast,
permanent storage. CompactFlash, SmartMedia and PCMCIA cards are all types of
Flash memory.
 DVD-ROM - DVD-ROM (digital versatile disc, read-only memory) is similar to CDROM but is capable of holding much more information.
Ports
 Parallel - This port is commonly used to connect a printer.
 Serial - This port is typically used to connect an external modem.
 Universal Serial Bus (USB) - Quickly becoming the most popular external connection, USB ports
offer power and versatility and are incredibly easy to use.
 FireWire (IEEE 1394) - FireWire is a very popular method of connecting digital-video devices, such
as camcorders or digital cameras, to your computer.
Internet/Network
 Modem - This is the standard method of connecting to the Internet.
 Local area network (LAN) card - This is used by many computers, particularly those in an Ethernet
office network, to connected to each other.
 Cable modem - This type of modem uses the cable TV system in your home to connect to the
Internet.
 Digital Subscriber Line (DSL) modem - This is a high-speed connection that works over a standard
telephone line.
 Very high bit-rate DSL (VDSL) modem - A newer variation of DSL, VDSL requires that your phone
line have fiber-optic cables.
Now that you are familiar with the parts of a PC, let's see what happens in a typical computer session.
How MP3 Files Work
The MP3 movement is one of the most amazing phenomena that the music industry has ever seen. Unlike
other movements -- for example, the introduction of the cassette tape or the CD -- the MP3 movement started
42
not with the industry itself but with a huge audience of music lovers on the Internet. The MP3 format for digital
music has had, and will continue to have, a huge impact on how people collect, listen to and distribute music.
If you have ever wondered how MP3 files work, or if you have heard about MP3 files and wondered how to use
them yourself, then this article is for you! In this article, you will learn about the MP3 file format and how you
can start downloading, listening to and saving MP3 files onto CDs
Using the MP3 Format
Knowing about the MP3 format isn't half as interesting as using it. The MP3 movement -- consisting of the MP3
format and the Web's ability to advertise and distribute MP3 files -- has done several things for music:
 It has made it easy for anyone to distribute music at nearly no cost (or for free).
 It has made it easy for anyone to find music and access it instantly.
 It has taught people a great deal about manipulating sound on a computer.
Technology has made it easier to download and play your
favorite music.
That third one was accidental but important. A big part of the MP3 movement is the fact that it has brought an
incredible array of powerful tools to desktop computers and given people a reason to learn how they work.
Because of these tools, it is now extremely easy for you to:







Download an MP3 file from a Web site and play it
Rip a song from a music CD and play it directly or encode it as an MP3 file
Record a song yourself, convert it to an MP3 file and make it available to the world
Convert MP3 files into CD files and create your own audio CDs from MP3 files on the Web
Rip songs off of various music CDs and recombine them into your own custom CDs
Store hundreds of MP3 files on data CDs
Load MP3 files into tiny portable players and listen to them wherever you go
43
To do all of these amazing things, all you need is a computer with a sound card and speakers, an Internet
connection, a CD-R drive to create CDs and an MP3 player. If you simply want to download MP3 files from the
Web and listen to them, then all you need is a computer with a sound card and speakers and an Internet
connection -- things you probably already have!
Let's look at many of the different things you can do with MP3 files and the software that makes it possible.
Downloading and Listening
If you would like to download and then listen to MP3 files on your computer, then you need:
 A computer
 A sound card and speakers for the computer (If your computer has speakers, it has a sound card.)
 An Internet connection (If you are browsing the Web to read this article, then you have an Internet
connection and it is working fine.)
 An MP3 player (a software application you can download from the Web in 10 minutes)
If you have recently purchased a new computer, chances are it already has software that can play MP3 files
installed on its hard disk. The easiest way to find out if you already have an MP3 player installed is to download
an MP3 file and try to double-click on it. If it plays, you are set. If not, you need to download a player, which is
very easy to do.
There are literally thousands of sites on the Web where you can download MP3 files. (Click here to do a search
for MP3 download sites.) Go to one of these sites, find a song and download it to your hard disk (most MP3
sites let you either listen to the song as a streaming file or download it -- you want to download). Most songs
range between 2 and 4 MB, so it will take 10 to 15 minutes unless you have a high-speed Internet connection.
Once the song has finished downloading, try to double-click on the file and see what happens. If your computer
plays it, then you are set.
If you find that you cannot play it, then you need to download an MP3 player. There are dozens of players
available, and most of them are free or shareware (shareware is extremely inexpensive). One of the most
popular is WinAmp, which you can download from www.winamp.com.
44
You are now ready to begin collecting MP3 files and saving them on your computer. Many people have
hundreds of songs they have collected, and they create jukebox-like playlists so that their computer can play
them all day long!
Taking the Files With You
Many people who start collecting MP3 files find that they want to listen to them in all kinds of places. Small,
portable MP3 players answer this need. These players are like portable cassette players except that they are
smaller.
These players plug into your computer's parallel, FireWire or USB port to transfer the data, and a software
application lets you transfer your MP3s into the player by simply dragging the files. See How MP3 Players Work
for details.
1.
2.
3.
4.
5.
6.
7.
MOTHERBOARD
CPU
RAM
VIDEO CARD
POWER SUPPLY
HARD DISK
OPTICAL DRIVE
How FireWire Works
You have probably heard the term FireWire if you have any interest in digital video -- or maybe you know it as
Sony i.Link or as IEEE 1394, the offical name for the standard. FireWire is a way to connect different pieces of
equipment so they can easily and quickly share information.
Originally created by Apple and standardized in 1995 as the specification IEEE 1394 High Performance Serial
Bus, FireWire is very similar to Universal Serial Bus (USB). The designers of FireWire had several particular
goals in mind when they created the standard:








Fast transfer of data
Ability to put lots of devices on the bus
Ease of use
Hot-pluggable ability
Provision of power through the cable
Plug-and-play performance
Low cabling cost
Low implementation cost
In this article, you will learn exactly what FireWire is, how it works and why you might want to use it.
45
What is FireWire?
FireWire is a method of transferring information between digital devices,
especially audio and video equipment. Also known as IEEE 1394, FireWire is
fast -- the latest version achieves speeds up to 800 Mbps. At some time in the
future, that number is expected to jump to an unbelievable 3.2 Gbps when
manufacturers overhaul the current FireWire cables.
You can connect up to 63 devices to a FireWire bus. Windows operating
systems (98 and later) and Mac OS (8.6 and later) both support it.
Let's say you have your digital camcorder connected to your home computer.
FireWire 400 sockets
When your computer powers up, it queries all of the devices connected to the
bus and assigns each one an address, a process called enumeration. FireWire is plug-and-play, so if you
connect a new FireWire device to your computer, the operating system auto-detects it and asks for the driver
disc. If you've already installed the device, the computer activates it and starts talking to it. FireWire devices are
hot pluggable, which means they can be connected and disconnected at any time, even with the power on.
Now let's take a look at FireWire's specifications.
FireWire Specifications
The original FireWire specification, FireWire 400 (1394a), was faster than USB when it came out. FireWire 400
is still in use today and features:
 Transfer rates of up to 400 Mbps
 Maximum distance between devices of 4.5 meters (cable length)
The release of USB 2.0 -- featuring transfer speeds up to 480 Mbps and up to 5 meters between devices -closed the gap between these competing standards. But in 2002, FireWire 800 (1394b) started showing up in
consumer devices, and USB 2.0 was left in the dust. FireWire 800 is capable of:
 Transfer rates up to 800 Mbps
 Maximum distance between devices of 100 meters (cable length)
The faster 1394b standard is backward-compatible with 1394a.
In the next section, we'll get deeper into the FireWire vs. USB debate.
FireWire vs. USB
The key difference between FireWire and USB is that FireWire is intended for devices working with a lot more
data -- things like camcorders, DVD players and digital audio equipment. FireWire and USB share a number of
characteristics but differ in some important ways.
46
Here's a summary:
Feature
USB
FireWire
1.1
2.0
400
800
Data transfer rate
12 Mbps
480 Mbps
400 Mbps
800 Mbps
Number of devices
127
127
63
63
Plug and play
Yes
Yes
Yes
Yes
Hot-pluggable
Yes
Yes
Yes
Yes
Isochronous devices
Yes
Yes
Yes
Yes
Bus power
Yes
Yes
Yes
Yes
Bus termination required
No
No
No
No
Bus type
Serial
Serial
Serial
Serial
Cable type
Twisted pair (4
wires: 2 power, 1
twisted-pair set)
Twisted pair (6
Twisted pair (4 wires: 2
wires: 2 power,
power, 1 twisted-pair
2 twisted-pair
set)
sets)
Networkable
Yes - host-based
Yes - host-based
Yes - peer-topeer
Yes - peer-topeer
Network topology
Hub
Hub
Daisy chain
Daisy chain
Twisted pair (8
wires: 2 power,
2 twisted-pair
sets, 2 ground)
As you can see, the two are a lot alike. Implementing FireWire costs a little more than USB, which led to the
adoption of USB as the standard for connecting most peripherals that do not require a high-speed bus.
Speed aside, the big difference between FireWire and USB 2.0 is that USB 2.0 is host-based, meaning that
devices must connect to a computer in order to communicate. FireWire is peer-to-peer, meaning that two
FireWire cameras can talk to each other without going through a computer.
Now let's get back to the implementation of FireWire. How do you connect?
FireWire Cables and Connectors
FireWire devices can be powered or unpowered. FireWire allows devices to draw their power from their
connection. Two power conductors in the cable can supply power (8 to 30 volts, 1.5 amps maximum) from the
computer to an unpowered device. Two twisted pair sets carry the data in a FireWire 400 cable using a 6-pin
configuration.
Some smaller FireWire-enabled devices use 4-pin connectors to save space, omitting the two pins used to
supply power.
47
FireWire 800 cables use a 9-pin configuration. Six of those pins are the same
as the six pins in the 1394a connector (shown above). Two of the added pins
provide a "grounded shield" to protect the other wires from interference, and
the third added pin does nothing at this time [ref].
Because FireWire 800 is backward-compatible with FireWire 400, there are a
variety of adapters available to facilitate the combination of both standards on
the same bus. There are also two types of FireWire 800 ports available: a
"bilingual" port accomodates both FireWire standards, while a b-only port
accepts only a FireWire 800 connector.
Sending Data via FireWire
Photo courtesy HSW Shopper
FireWire adapter cable (9-pin
configuration on left)
FireWire uses 64-bit fixed addressing, based on the IEEE 1212 standard.
There are three parts to each packet of information sent by a device over
FireWire:
 A 10-bit bus ID that is used to determine which FireWire bus the data came from
 A 6-bit physical ID that identifies which device on the bus sent the data
 A 48-bit storage area that is capable of addressing 256 terabytes of information for each node
The bus ID and physical ID together comprise the 16-bit node ID, which allows for 64,000 nodes on a system.
Data can be sent through up to 16 hops (device to device). Hops occur when devices are daisy-chained
together. Look at the example below. The camcorder is connected to the external hard drive connected to
Computer A. Computer A is connected to Computer B, which in turn is connected to Computer C. It takes four
hops for Computer C to access the camera.
Assuming all of the devices in this setup are equipped with FireWire 800, the camcorder can be up to 400
meters from Computer C.
Now that we've seen how FireWire works, let's take a closer look at one of its most popular applications:
streaming digital video.
FireWire and Digital Video
FireWire really shines when it comes to digital video applications. Most digital video cameras or camcorders
now have a FireWire plug. When you attach a camcorder to a computer using FireWire, the connection is
amazing.
An important element of FireWire is the support of isochronous devices. In isochronous mode, data streams
between the device and the host in real-time with guaranteed bandwidth and no error correction. Essentially,
this means that a device like a digital camcorder can request that the host computer allocate enough bandwidth
48
for the camcorder to send uncompressed video in real-time to the computer. When the computer-to-camera
FireWire connection enters isochronous mode, the camera can send the video in a steady flow to the computer
without anything disrupting the process.
You can easily edit and create custom video projects using fast hard drives, a digital camcorder and a
computer. With the right software, the computer and the camera communicate, and the computer can download
all of the video automatically and with perfect digital clarity. Since the content is digital from start to finish, there
is no loss of quality as you work on successive generations.
For more information on FireWire and related topics, check out the links on the next page.
How Windows Vista Works
The first version of Microsoft Windows hit the market in 1983. But unlike today's versions of Windows, Windows
1.0 was not an operating system (OS). It was a graphical user interface that worked with an existing OS
called MS-DOS. Version 1.0 didn't look much like newer versions, either -- not even Windows 3.0, which many
people think of as the first real version of Windows. Its graphics were simpler and used fewer colors than
today's user interfaces, and its windows could not overlap.
Windows has changed considerably since then. In the last 20 years, Microsoft has released numerous fullfledged versions of the operating system. Sometimes, newer versions are significantly different from older ones,
such as the change from Windows 3.1 to Windows 95. Other new releases have seemed more like
enhancements or refinements of the older ones, such as the multiple consumer versions of the OS released
from 1995 to 2001.
Microsoft's newest version of its operating system is Windows Vista. For many users, upgrading to Vista won't
seem as dramatic as the upgrade from 3.1 to Windows 95. But Windows Vista has a number of new features,
both in the parts that you can see and the parts that you can't.
At its core, Windows Vista is still an operating system. It has two primary behind-the-scenes jobs:
 Managing hardware and software resources, including the processor, memory, storage and
additional devices
 Allowing programs to work with the computer's hardware
If all goes well, this work is usually invisible to the user, but it's essential to the computer's operation. You can
learn about these tasks in more detail in How Operating Systems Work.
But when many people think of operating systems, they think of the portion they can see -- the graphical user
interface (GUI). The GUI is what people use to interact with the hardware and software on the computer. In
Windows systems, features like the Start menu, the recycle bin and the visual representations of files and
folders are all part of the GUI.
Windows Vista's GUI is a 3-D interface called Windows Aero. Of the four editions of Windows Vista, three -Home Premium, Business and Ultimate -- support Windows Aero. Home Basic, the most scaled-down
edition of the OS, uses a less graphics-intensive GUI instead of Aero. The other editions can also use this basic
GUI, so people with older computers that can't support lots of 3-D graphics can still upgrade to Vista.
We'll take a closer look at the Aero GUI and other Vista features next.
Microsoft's Web site has more information on which features each edition includes.
Additional Editions
In addition to the four primary editions of Windows Vista, there are
two editions for special markets. Windows Vista Enterprise is
designed for very large businesses. Windows Vista Starter is a
basic Vista OS for use in emerging markets, such as developing
countries.
Windows Vista: Aero
49
In some ways, Windows Aero is similar to recent versions of the Windows GUI, like the one used in Windows
XP. Aero organizes information in on-screen windows and uses icons to represent files, folders and
applications. But Aero also has several features that you can think of as upgrades to the Windows XP GUI. Its
windows are three-dimensional objects that you can move and adjust in any direction. Aero Glass makes the
borders of each window translucent so you can see the desktop or other windows behind it. Microsoft asserts
that the clear border lets you focus on your work instead of on your interface [Source: Microsoft].
Photo courtesy © 2006 Microsoft Corporation. All rights reserved.
Aero Glass
Vista also replaces the simple, static icons that represent many files in older Windows GUIs with more
elaborate Live Icons. Live Icons give you up-to-date thumbnail previews of each file. When you look at a
document's Live Icon, you see what the document actually looks like rather than seeing an icon for the program
that created it. You can also look at the contents of files before opening them by using the Explorer preview
pane.
Similar thumbnails also replace the icons you see when you use the "alt" and "tab" keys to move through open
windows. Aero's more basic version of "alt + tab," called Flip, lets you choose from 2-D thumbnail previews on
a menu bar. Another feature, Flip 3D, lets you choose from three-dimensional, moving thumbnails rather than
2-D images. In addition, if you hover your mouse over items on your taskbar, you'll see 2-D thumbnails of each
window instead of text listing the applications and filenames.
Photo courtesy © 2006 Microsoft Corporation. All rights reserved.
Flip 3D
50
Many elements of the Aero GUI, including the Start menu and the windows themselves, incorporate new search
capabilities. While a computer is running, Vista scans the disc drive for changes and maintains a running index
of its files. You can search this index from multiple locations within the GUI. For example, rather than moving
your mouse through a series of cascading windows in the Start menu, you can simply type in the program or file
you're looking for. You can also create search folders -- saved searches that you can return to when you need
to find particular files or folders. Adding metadata, or tags, to your files can make these searches more
efficient. When you search for a file, the computer examines filenames, tags and document contents to find
relevant results.
Photo courtesy © 2006 Microsoft Corporation. All rights reserved.
The Start search menu
In addition to the GUI, Vista comes with several new applications. Different versions include different features,
but here's a sample of what's new:
 Sidebar allows you to access mini-applications called Gadgets. Sidebar is similar to Konfabulator
or Macintosh OS X's Dashboard, which call their mini-applications Widgets.
 Meeting Space is a teleconferencing program for small groups of Vista users.
 Speech Recognition lets users control their computers and create documents using their voices.
Vista has a speech-activated user interface as well as a general voice dictation application.
 Windows Mail replaces Outlook Express for home users and includes anti-phishing tools.
 Windows Calendar, also for home users, is an interactive calendar application. In addition to
allowing users to keep track of appointments, it can be used to send e-mail invitations to events.
Photo courtesy © 2006 Microsoft Corporation. All rights reserved.
Sidebar
51
Vista also has a few new tools intended to improve performance:
 SuperFetch pre-loads frequently-used applications into the memory so they can start up faster.
 ReadyBoost lets people add RAM to their system with a USB thumb drive.
 Sleep lets you quickly resume working by storing files that are currently in use. On desktop
computers, these files are saved in the computer's RAM and on the hard drive. On laptop
computers, the files are saved to the hard drive only when the battery power wanes.
Because of its new features, particularly its 3-D GUI, Vista has different hardware requirements than previous
versions of the OS. We'll look at these requirements and explore how Vista creates the 3-D desktop next.
WinFS
While developing Windows Vista, Microsoft planned to incorporate a new file system called WinFS. Short for
Windows Future System, WinFS stored data in a relational database. Rather than storing information in a series of
folders and subfolders, WinFS would create indexes of a drive's data. In August 2004, Microsoft announced that
WinFS would not be part of Vista. The company instead added new search capabilities to its existing file structure.
Windows Vista: Creating a 3-D Desktop
Windows Vista's desktop environment requires considerably more computer resources than previous versions
of the OS. For this reason, and to make the OS more stable, Vista's graphics subsystem is different from its
predecessors.
First, Windows Vista uses a new graphics driver model, known as the Windows Display Driver Model
(WDDM). Previous Windows graphics drivers ran in kernel mode. They had direct access to the graphics
hardware, and their performance could affect the operating system. This is why graphics errors could cause the
entire system to stop responding. WDDM, however, runs primarily in user mode. It has little direct access to
the graphics hardware or to critical parts of the operating system. Microsoft instituted a similar change to Vista's
audio subsystem as well. These changes should help make the OS more stable.
The WDDM manages the workload of the graphics processing unit (GPU). It allocates the video memory
required for different tasks, and it prioritizes applications that need access to the GPU. In other words, it helps
budget the computer's video processing resources. This is particularly important, since the OS and applications
that use lots of 3-D graphics have to share the computer's graphics resources.
Photo courtesy © 2006 Microsoft Corporation. All rights reserved.
Windows Vista desktop view
A driver called the Desktop Window Manager (DWM) is part of the WDDM. This driver is responsible for
updating what you see on the desktop. The DWM draws all of the objects you see on your screen and holds
them in a buffer until you need them. By keeping different desktop views in a buffer, the DWM should help
prevent the blank square of space that often appears when programs stop responding. The DWM creates the
thumbnails used in Flip and Flip-3D, and it can scale on-screen images to fill high-resolution monitors.
52
Although the WDDM is central to creating the windows you use to access your applications, it doesn't
communicate with those programs directly. Instead, it interacts with programs through an application
programming interface (API). APIs help hardware and software communicate more efficiently by providing
sets of instructions for complex tasks. Windows Vista can use DirectX 9 as its API, although a new version,
DirectX 10, is a built-in, exclusive part of the OS.
All this 3-D rendering requires lots of processing power. To use Aero and some of the more hardware-intensive
features of Windows Vista, a computer must be Premium Ready. It has to have enough system and graphics
memory to handle constant creation and manipulation of 3-D images. This is why the requirements for a
Premium Ready computer sound like what you'd expect from a 3-D game. It must have:




A 1 GHz 32-bit or 64-bit processor
1 GB of system memory
A 40 GB hard drive with at least 15 GB of free space
At least 128 MB of graphics memory
The computer also has to support DirectX 9, have a DVD-ROM drive and have access to the Internet. Microsoft
has a list of all of the necessary components for a Premium Ready system.
If you're considering upgrading to Windows Vista and want to use the Aero interface, you should keep in mind
that these are the minimum requirements. If your computer meets exactly these specifications, it will be able to
create the 3-D interface. However, it may bog down if you're multitasking or playing image-intensive games. If
you hope to run Vista on a laptop or a desktop that doesn't have a dedicated video card, you may find that the
GUI's benefits don't outweigh the strain it puts on your system resources. To get optimal performance from the
Aero user interface, a computer needs to exceed the minimum recommendations, including a separate video
card with its own graphics memory.
Microsoft has published different minimum requirements for computers using the basic interface. They include:
 An 800 MHz or better modern processor
 512 MB of system memory
 A graphics processor that supports DirectX 9
Microsoft has also made some changes to how Vista handles networking and security. We'll look at these
changes in the next section.
Changing the Volume
You may have had the experience of trying to talk to someone over IM while listening to music on your computer.
Sometimes, your choices are to hear your IM notification sounds blaring over your music or to turn them off entirely.
Windows Vista eliminates this issue by allowing people to change the outbound volume of each application.
Cap Bits
Previous versions of DirectX used capability bits, or cap bits, to describe different DirectX features. Hardware did
not necessarily have to support all of the cap bits to be DirectX compliant. For this reason, video cards and other
components didn't always work properly even if they were DirectX compliant. DirectX 10 does away with this system,
designating only three features as optional.
Windows Vista: Networking and Security
In the past, computer networks primarily existed in schools, businesses and computer enthusiasts' homes. But
today, many households have several computers that need to share files, printers and connections to the
Internet. Unlike most businesses, many average home users do not have a networking expert to set up and
maintain their networks.
For this reason, Windows Vista includes several network setup wizards, which walk users through creating
networks and sharing devices. It also has several built-in network tools that are accessible through a Network
Center:
 Network Explorer lets users find files on networked computers and move them from to place. It's
similar to other Windows Explorers that let people find files on their own computers.
 Network Map creates a visual map of all the computers and devices on the network.
53
Vista also includes a Network Awareness feature for people who need to use their computers in multiple
locations. Network Awareness detects which network a person's computer is using and applies the appropriate
settings.
Photo courtesy © 2006 Microsoft Corporation. All rights reserved.
The Network Center
Vista also includes tools to help people maintain and repair their own networks. The Network Diagnostics
feature can detect and repair some network issues on its own. It can also walk users through the necessary
steps to restore their network connections. To do this, it uses a collection of tools that use the Windows
Diagnostic Infrastructure (WDI).
The WDI provides the structure for several components, including the Network Diagnostics Framework
(NDF) and several APIs. The NDF identifies and troubleshoots client-side network issues using a Network
Diagnostics Engine as well as Microsoft and third-party helper classes. The helper classes are
troubleshooting protocols, and the Network Diagnostic Engine communicates with them through the helper
class API. Applications that need to access the Internet can also use APIs to access Vista's troubleshooting
capabilities.
Other changes to Vista should improve computers' security once they're connected to a network or the Internet.
Some experts blame the Windows kernel for previous issues with security [Source: Extreme Tech]. Although
Vista uses essentially the same kernel as previous versions of Windows, Microsoft has made some changes to
how applications interact with it. In addition to making the computer more stable, this change will also make it
more difficult for people to write malicious code designed to exploit applications and affect the kernel.
Vista also includes applications and tools that people can use to make their systems more secure. As with
previous versions of Windows, Vista can check for, download and install security updates automatically. In
addition, it has several new security features:
 User Account Control (UAC) lets each Windows Vista user for a particular computer set up his
own account. A user with administrative privileges can determine what kind of applications
different accounts can install and what kind of changes they can make to the computer's setup. In
many cases, installing software and making changes to the operating system requires an
administrator's password.
 UAC also lets parents use parental controls to manage what kind of games their children can play
and what kind of Web content they can view. Parents can also set time limits for computer use.
 User Account Control, Windows Firewall, Windows Defender and the Malicious Software
Removal Tool improve system security and help prevent and remove viruses and Spyware.
However, many industry experts advise users to install additional virus protection.
54
Photo courtesy © 2006 Microsoft Corporation. All rights reserved.
The Family Safety Center
Although Microsoft has presented Vista as safer and more secure than previous versions of Windows, the new
OS is not without controversy. Critics have pointed out that many of its features, including search, Sidebar and
preview pane functions, already exist in other operating systems, like Linux and Macintosh OS X. Beta testers
have described the UAC password requirements as invasive and annoying. Some claim that the improved
security that comes from changes to how applications interact with the kernel will be short-lived. Vista has also
been accused of antitrust violations in several countries, particularly because of its integrated malware removal
tools.
Other criticism is laptop-specific. Aero's hardware requirements for 3-D rendering may drain laptop batteries
more quickly than older versions of Windows. The sleep state may also drain laptop batteries when the laptops
are not in use.
Vista hit the market for volume license buyers on November 30, 2006, and it became available to the public on
January 30, 2007. With the 3-D GUI and related hardware requirements, it has the potential to change how
people shop for computers, especially when it comes to graphics hardware. Only time will tell whether the
differences between Windows Vista and prior versions make it a more stable, secure OS or whether its most
significant changes are cosmetic.
Check out Microsoft's site for more detailed information about Windows Vista's features and costs. See the
links on the next page for more information on computers, operating systems and related topics.
What's a Kernel?
A kernel is a small but integral piece of an operating system. It's usually the first piece to load into the computer's
memory, and it stays there while the computer runs. Many other applications and devices rely on the kernel
extensively, so problems with it can cause system-wide issues.
Choosing Between an Inverter and a Generator
An engine-powered generator is an easy way to supply your house with emergency power. They are relatively
inexpensive (typical price for a 5,000-watt generator ranges between $600 and $1,200), produce clean, 120- or
240-volt sine-wave power, and consume only about a gallon of gas every two hours or so (at 1,000-watt
output). You can also purchase generators that run off of diesel fuel or propane.
55
A 5,000-watt gasoline-powered generator
This generator has a 10-horsepower engine and a 5,000-watt generator with a surge rating of
6,500 watts. The gas tank (black, mounted across the top of the frame) holds 7 gallons and runs
about 12 hours at 1,000-watt usage levels. This generator produces 120-volt or 240-volt output. It
is shown with its grounding cable and the 240-volt cable that plugs it into the house's circuit panel.
The disadvantages of engine-powered generators include:
 Fuel storage
 Noise (especially the less-expensive models)
 Engine maintenance
Fuel storage can be a nuisance -- gasoline cannot be stored for more than a month or so unless you use a fuel
stabilizing chemical, and even then the shelf-life is relatively short. You need to rotate your inventory on a
regular basis to avoid problems.
Here at the Brain household we have a 5,000-watt generator. We are able to run just about everything in the
house -- including the well pump, water heater and refrigerator -- with the generator. The only thing we cannot
run is the heat pump, so we have gas logs as a backup heat source. We do stagger our usage, but that is not a
big problem for us. For example, we will run the refrigerator for an hour and then turn it off to run the well pump.
An inverter is an electrical device that converts 12-volt power into 120-volt power. Typically you run an inverter
off of your car's battery or off of a deep-cycle battery that you buy specifically to power the inverter. An inverter
is a very easy and inexpensive solution if you can keep your power demands in the 200-watt range. If you are
willing to build a more elaborate system, inverters can be a good option up to about 2,500 watts, although they
tend to get expensive at that point (a 2,500-watt inverter might cost $600 to $1,000, and then you need to buy a
number of deep-cycle batteries and a charging system). Inverters have two main advantages:
 They are silent
 They are maintenance-free (when you operate them from your car's battery -- if you build your own
deep-cycle battery bank you will have to maintain the batteries).
Here are some things to think about when considering an inverter:
 You can buy a small 150- or 300-watt quasi-sine-wave inverter for
about $50 and plug it into your car's lighter socket. It can operate
several light bulbs, a radio, a small TV, etc.
 A car's battery has a reserve capacity rating. A typical rating is 80
minutes, which means the battery can supply 25 amps at 12
volts for 80 minutes. If you consume 120 watts continuously, that
means that you are draining about 10 amps from your car's
battery continuously. A typical car battery can supply power at
that level for perhaps three hours. A deep-cycle battery can
supply power at that level for six or eight hours. Then you will
need to recharge the battery (which takes awhile). However, if
56
you are running two compact fluorescent bulbs at 15 watts each, total consumption is only 30
watts, or 2.5 amps at 12 volts. A car battery can supply power for about 12 hours at that level. A
deep-cycle battery can supply power for a day or two at that level.
 A typical car's alternator can supply only about 700 watts maximum. To run an inverter with a
capacity greater than 300 watts from a car, you need to connect it
directly to the car's battery with cables, and you will need to run
the car's engine continuously. At that point, it would be much
more efficient to buy a gasoline generator.
From this discussion you can see that an inverter only makes sense for
very small power loads over relatively short time frames. You can build a
large and elaborate battery system to run your inverter if you choose, but
that can get expensive.
(Note that a large battery bank connected to an inverter is an important part
of most home-scale solar power systems. Solar panels are used to
recharge the batteries in that case. See How Solar Cells Work for details.)
Here at the Brain household we have a 140-watt inverter. We run the
generator during the day. At night we use the inverter hooked to the car to
power one or two compact fluorescent bulbs that provide light in the house.
What is the difference between a normal lead-acid car battery and a deep cycle
battery?
People who have recreational vehicles (RVs) and boats are familiar with deep cycle batteries. These batteries
are also common in golf carts and large solar power systems (the sun produces power during the day and the
batteries store some of the power for use at night). If you have read the article How Emergency Power Systems
Work, then you also know that an alternative to gasoline-powered generators is an inverter powered by one or
more deep cycle batteries.
Both car batteries and deep cycle batteries are lead-acid batteries that use exactly the same chemistry for their
operation (see How Batteries Work for more information). The difference is in the way that the batteries
optimize their design:
 A car's battery is designed to provide a very large amount of current for a short period of
time. This surge of current is needed to turn the engine over during starting. Once the engine
starts, the alternator provides all the power that the car needs, so a car battery may go through its
entire life without ever being drained more than 20 percent of its total capacity. Used in this way, a
car battery can last a number of years. To achieve a large amount of current, a car battery uses
thin plates in order to increase its surface area.
 A deep cycle battery is designed to provide a steady amount of current over a long period of
time. A deep cycle battery can provide a surge when needed, but nothing like the surge a car
battery can. A deep cycle battery is also designed to be deeply discharged over and over again
(something that would ruin a car battery very quickly). To accomplish this, a deep cycle battery
uses thicker plates.
A car battery typically has two ratings:
 CCA (Cold Cranking Amps) - The number of amps that the battery can produce at 32 degrees F (0
degrees C) for 30 seconds
 RC (Reserve Capacity) - The number of minutes that the battery can deliver 25 amps while keeping
its voltage above 10.5 volts
Typically, a deep cycle battery will have two or three times the RC of a car battery, but will deliver one-half or
three-quarters the CCAs. In addition, a deep cycle battery can withstand several hundred total
discharge/recharge cycles, while a car battery is not designed to be totally discharged.
PROFESSIONAL QUALITY WHEELED CHARGER STATION
57
o
o
o
o
Jumps starts vehicle in one minute, charges in one hour!
4, 10, 20 or 50-amp charge rate—one minute engine start at 150 amps
Digital display indicates charge rate, operating mode, fault codes, battery voltage and
"FUL" when charged
Fully automatic with float mode monitoring
Using high frequency power conversion technology, this "smart", microprocessor controlled
charger features built-in battery reconditioning, built-in digital diagnostics, automatic temperature
compensation and battery type selection. It compensates for low AC power when an extension
cord is used. Alternator and battery voltage check. For safety, there's a reverse polarity indicator
and reverse polarity and internal short circuit protection. Cables and clamps are self storing. High
frequency 3-stage switch mode and automatic rapid charging.
Access
Database Creation and Design
Covers essential elements of database manipulation
Hands-on; 10 hours over 4 days
Authorized Microsoft IT Academy
Instructor-led, fast-paced continuing education
Suggested For:
 Database Administrators
 Clerical Personnel
 Office Assistants
 Programmers
 Executives
 Software Developers
Autocad
Computer Aided Design at its finest!
58
Covers essential drawing and editing techniques
Hands-on; 10 hours over 4 days
Instructor-led, fast-paced continuing education
Taught using Autocad LT
Suggested For:
 Architects
 Draftspeople
 Engineers
 Interior Decorators
 Furniture Designers
 Landscape Architects

Solution Developers
Frontpage
Internet Web Page Creation & Design
Covers practical site design techniques
Hands-on; 10 hours over 4 days
Instructor-led, fast-paced continuing education
Authorized Microsoft IT Academy
Suggested For:
 Consumers
 Merchants
 Those with distant loved ones
 Mobility Challenged
 Clerical Personnel
 Office Staff
 Software Developers
 Programmers

Excel
Spreadsheet Creation and Design
Covers useful spreadsheet techniques and shortcuts
Hands-on; 10 hours over 4 days
Instructor-led, fast-paced continuing education
Authorized Microsoft IT Academy
Suggested For:
 Bookkeepers
 Accountants
 Clerical Personnel
 Office Assistants
 Programmers
 Software Developers
 Executives

Salespeople
Executives
Office Suite
Word Processing, Presentations, Spreadsheets
& Database all in one professional software package
Hands-on; 40 hours over 2 weeks
Covers the essentials of the primary components
Instructor-led, fast-paced continuing education
Authorized Microsoft IT Academy
Suggested For:
 Bookkeepers
 Accountants
 Clerical Personnel
 Office Assistants
 Programmers
 Software Developers
 Executives
 Students
59
 Teachers
 IT Professionals
Powerpoint
Presentations and Slide Design
Covers tricks traps and shortcuts
Hands-on; 10 hours over 4 days
Instructor-led, fast-paced continuing education
Authorized Microsoft IT Academy
Suggested For:
 Clerical Personnel
 Office Assistants
 Programmers
 Software Developers
 Researchers
 Sales Persons
 Teachers

Windows For Beginners
This is the place to start!
Covers the essentials of operating a computer
Hands-on; 10 hours over 4 days
Instructor-led, fast-paced continuing education
Authorized Microsoft IT Academy
Suggested For:
 Clerical Personnel
 Office Assistants
 Programmers
 Software Developers
 Executives
 Students
 Teachers
 IT Professionals
 Secretaries

All Computer Users
IT Professionals
Word
Quickbooks
Throw away your ledger book!
Covers the essentials of automated bookkeeping
Hands-on; 10 hours over 4 days
Intuit experts on staff
Instructor-led, fast-paced continuing education
Suggested For:
 Bookkeepers
 Accountants
 Clerical Personnel
 Office Assistants
 Programmers
 Software Developers
 Executives
 Buyers

Word Processing at its finest!
Covers tricks, traps and shortcuts
Authorized Microsoft IT Academy
Instructor-led, fast-paced continuing education
Hands-on; 10 hours over 4 days
Suggested For:
 Clerical Personnel
 Office Assistants
 Programmers
 Software Developers
 Executives
 Students
 Teachers
 IT Professionals

Secretaries
A/R Personnel
60
Internet
Web Usage and Techniques
Covers essentials that apply to all web surfers
Includes lots of interesting sites of interest to all
Hands-on; 10 hours over 4 days
Authorized Microsoft IT Academy
Instructor-led, fast-paced continuing education





Clerical Personnel
Office Staff
Software Developers
Programmers
Executives
Suggested For:
 Consumers
 Merchants
 Those with distant loved ones
 Mobility Challenged
PC Introduction
Introduction to Windows XP and Windows Vista
Typing Tutor
English
Spanish (optional)
French (optional)
Introduction to Microsoft Office
 Introduction to Microsoft Word
 Introduction to Microsoft PowerPoint
Introduction to Internet
 Create and manage your email with MSN and Yahoo Messenger
 Share documents online, photos, videos and more…
Website Design Class
Learn how to:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Create and Design your own Web Site & Web Page
Create your own Virtual Online Business
Increase sales & traffic to your website immediately
Come up on the 1st Page of (Google and Yahoo)
Create your Brand/Logo and get it recognized Worldwide
Create a Powerful Domain Name
Sell your Products & Services thru (eBay)
Attract and retain more Customers through Niche Marketing
Worldwide recognition of your business
Sell More Products or Services through E-Commerce
Market with infomercials on (Youtube and Myspace)
Email Campaign - contact thousands of new customers
61
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
Create a Bilingual or Multilingual Website to attract buyers
Cross-Sell new products utilizing online marketing strategies
Create a 24 hour Online Store
Add a Credit Card Merchant Service (PayPal)
Upload a Video Recording of your company's services
Upload an Audio Recording of your Company's services
Podcast - Broadcast upcoming products & events
Create the illusion of a Fortune 500 company
Add powerful Links that generate more viewer traffic
Maximize Search Engine Optimization (SEO) techniques
Make money thru Affiliate Partnerships
Edit and Upload Photos & Images to your Website
Create a corporate image with an 800 number
Track your Website Traffic & increase its performance
Webinar -Give an Online Presentation of your product
Information Technology
Programs
1. Associate in IT/CS
2. Bachelor in IT/CS
3. Masters in IT/CS
4. PhD in IT/CS
5. Certificates in IT
6. C++ Programming
7. Cisco Certifications
8. Cisco - CCNA
9. Cisco - CCNP
10. CIW Certification
11. CompTIA Certifications
12. CompTIA - A+
13. CompTIA - Network+/i-Net+
14. Computer Networking
15. Computer Programming
16. Computer Science
17. Database Administration
18. Desktop Applications
19. Information Assurance
20. Information Technology
21. Java Programming
22. Microsoft Certifications
23. Microsoft - MCAD
24. Microsoft - MCDBA
25. Microsoft - MCSA
26. Microsoft - MCSD
27. Microsoft - MCSE
28. Microsoft - MOUS/MOS
29. Network Administration
30. Network Security
31. Oracle Certifications
32. Oracle - OCP
33. Repairs & Tech Support
34. Sun Certifications
35. Telecom/Wireless
36. Visual Basic Programming
37. Webmaster
38. Web Development
Art & Design Degrees
39. Architecture
40. Film & Television Production
41. Fine Arts
42. Graphic Design
43. Interior Design
44. Multimedia Design
62
45. Photography
46. Video Game Design
47. Visual Communications
48. Web Design
Repairs & Tech Support
Information Technology specialists focusing on Repairs and Technical Support utilize interpersonal
communication skills to effectively deal with customers directly, providing assistance and step-by-step
instruction to solve computer and technology related problems. Repair and Support technicians possess a
comprehensive understanding of information systems and technology and are qualified to troubleshoot
computer software, hardware, and electronic devices. Generally, Repair and Tech Support professionals
possess a minimum-level industry certification and receive training to improve proficiency in personal computer
manipulation and application. Many professionals in this field with degrees hold an Associate's or Bachelor's in
a related field prior to obtaining Repair/Technical Support certification. Higher levels of education yield higher
income potential with the possibility of advancement to senior-level support and management. Salaries
typically average between $35,000 to $65,000 although senior positions can earn upwards of $90,000. To
learn more about education in Computer Repair and Computer Tech Support, request free information
packets from the schools listed below.
List of web browsers
This is a table of personal computer web browsers by year of release of major version, in chronological
order, with the approximate number of worldwide Internet users in millions. Note that Internet user data is
related to the entire market, not the versions released in that year. The increased growth of the Internet in
the 1990s and 2000s means that current browsers with small market shares have more total users than the
entire market early on. For example, 90% market share in 1997 would be roughly 60 million users, but by
the start of 2007 9% market share would equate to over 90 million users.[1]
Year
Web Browsers
1991
1992
1993
1994
WorldWideWeb (Nexus)
ViolaWWW, Erwise, MidasWWW, MacWWW (Samba)
Mosaic, Cello[2], Lynx 2.0, Arena, AMosaic 1.0
IBM WebExplorer, Netscape Navigator, SlipKnot 1.0, MacWeb, IBrowse, Agora (Argo), Minuet
Internet Explorer 1, Netscape Navigator 2.0, OmniWeb, UdiWWW[3], WebRouser[4], Internet Explorer
2, Grail
Arachne 1.0, Internet Explorer 3.0, Netscape Navigator 3.0, Opera 2.0,
PowerBrowser 1.5[5], Cyberdog, Amaya 0.9[6], AWeb, Voyager
Internet Explorer 4.0, Netscape Navigator 4.0, Netscape Communicator 4.0, Opera 3.0[7], Amaya 1.0[6]
iCab, Mozilla
Amaya 2.0[6], Mozilla M3, Internet Explorer 5.0
Konqueror, Netscape 6, Opera 4[8], Opera 5[9], K-Meleon 0.2, Amaya 3.0[6], Amaya 4.0[6]
Internet Explorer 6, Galeon 1.0, Opera 6[10], Amaya 5.0[6]
Netscape 7, Mozilla 1.0, Phoenix 0.1, Links 2.0, Amaya 6.0[6], Amaya 7.0[6]
Opera 7[11], Safari 1.0, Epiphany 1.0, Amaya 8.0[6]
Firefox 1.0, Netscape Browser, OmniWeb 5.0
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Internet
Users (in
millions)[1]
16
36
70
147
248
361
513
587
719
817
63
2005
2006
2007
2008
2009
2010
Safari 2.0, Netscape Browser 8.0, Opera 8.[12], Epiphany1.8, Amaya 9.0[6], AOL Explorer1.0, Maxthon
1.0, Shiira 1.0
SeaMonkey 1.0, K-Meleon 1.0, Galeon 2.0, Camino 1.0, Firefox 2.0, Avant 11, iCab 3, Opera 9[13],
Internet Explorer 7, Sputnik
Maxthon 2.0, Netscape Navigator 9, NetSurf 1.0, Flock 1.0, Safari 3.0, Conkeror
Konqueror 4, Safari 3.1, Opera 9.5[14], Firefox 3, Amaya 10.0[6], Flock 2, Chrome 1, Amaya 11.0[6]
Internet Explorer 8, Chrome 2, Safari 4, Opera 10[15], Chrome 3, SeaMonkey 2, Camino 2, Firefox 3.5
Firefox 3.6, Chrome 4 through Chrome 8, Opera 10.50[16], Safari 5, Opera 11
1018
1093
1262
1565
1734
Notable browsers
In order of release:










WorldWideWeb, February 26, 1991
Mosaic, April 22, 1993
Netscape Navigator and Netscape Communicator, October 13, 1994
Internet Explorer 1, August 16, 1995
Opera, 1996, see History of the Opera web browser
Mozilla Navigator, June 5, 2002[17]
Safari, January 7, 2003
Mozilla Firefox, November 9, 2004
Google Chrome, September 2, 2008
An operating system (OS) is software, consisting of programs and data, that runs on computers and
manages computer hardware resources[1] and provides common services for efficient execution of various
application software.
For hardware functions such as input and output and memory allocation, the operating system acts as an
intermediary between application programs and the computer hardware,[2][3] although the application code
is usually executed directly by the hardware, but will frequently call the OS or be interrupted by it.
Operating systems are found on almost any device that contains a computer—from cellular phones and
video game consoles to supercomputers and web servers.
Examples of popular modern operating systems for personal computers are Microsoft Windows, Mac OS
X, and GNU/Linux.[4]
List of Microsoft operating systems
Before Windows



Xenix
MS-DOS
MSX-DOS
Windows
Main article: List of Microsoft Windows versions
64



Windows 1.0
Windows 2.0
Windows 3.x
Windows NT line
Further information: Windows NT









Windows NT 3.1
Windows NT 3.5
Windows NT 3.51
Windows NT 4.0
Windows 2000
o Professional
o Server
o Advanced Server
o Datacenter Server
Windows XP (full details)
o Starter Edition (16 editions for each of 16 countries)
o Home Edition
o Home Edition N (European market)
o Home Edition K (South Korean market)
o Home Edition KN (South Korean market)
o Home Edition for Subscription Computers
o Home Edition for Prepaid Computers
o Professional Edition
o Professional Edition N (European market)
o Professional Edition K (South Korean market)
o Professional Edition KN (South Korean market)
o 64-bit Edition
o Professional x64 Edition
o Media Center Edition
o Tablet PC Edition
o XP for Embedded Systems
o XP Embedded
o Embedded for Point of Service
o Windows Fundamentals For Legacy PCs
Windows Server 2003
o Small Business Server
o Web Edition
o Standard Edition
o Enterprise Edition
o Datacenter Edition
o Storage Server
o Windows Home Server
Windows Vista (full details)
o Starter
o Home Basic
o Home Basic N (European market)
65
o
o
o
o
o




Home Premium
Business
Business N (European market)
Enterprise
Ultimate
Windows Server 2008
o Web Server
o Standard Edition
o Enterprise Edition
o Datacenter Edition
o for Itanium-based Systems
Windows 7 (full details)
o Starter
o Home Basic
o Home Premium
o Home Premium N (European market)
o Professional
o Professional N (European market)
o Enterprise
o Ultimate
o Ultimate N (European market)
Windows 9x line



Windows 95
Windows 98
Windows Me
Windows Mobile computing









Windows CE
Windows Mobile
Microsoft Windows Mobile 2003 Second Edition
Microsoft Windows Mobile 2005
Windows CE 3.0
Windows CE 4.0
Windows CE 5.0
Windows Mobile 6
Windows Mobile 6.5
Future Windows Versions

Windows 8
Other operating systems in development

Singularity (operating system)
66

Windows Phone 7
Never eventuated
Windows






Windows Chicago
Windows Neptune
Windows NT 5.0
Windows Nashville
Windows Whistler
Windows LongHorn
OS/2



MS OS/2 2.0
MS OS/2 3.0
MS OS/2 4.0
Mac OS X
Mac OS X (pronounced /ˈmæk ˌoʊ ˌɛs ˈtɛn/ mak oh es ten)[6] is a series of Unix-based operating systems and
graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, Mac OS X has been included with
all new Macintosh computer systems. It is the successor to Mac OS 9, released in 1999, the final release of the
"classic" Mac OS, which had been Apple's primary operating system since 1984.
Mac OS X, whose X is the Roman numeral for 10 and is a prominent part of its brand identity, is a Unixbased graphical operating system,[7] built on technologies developed at NeXT between the second half of
the 1980s and Apple's purchase of the company in late 1996. From its sixth release Mac OS X v10.5
"Leopard" and onwards, every release of Mac OS X gained UNIX 03 certification while running on Intel
processors.[3][4]
The first version released was Mac OS X Server 1.0 in 1999, and a desktop-oriented version, Mac OS X
v10.0 "Cheetah" followed on March 24, 2001. Releases of Mac OS X are named after big cats: for
example, Mac OS X v10.6 is usually referred to by Apple and users as "Snow Leopard". The server edition,
Mac OS X Server, is architecturally identical to its desktop counterpart, and includes tools to facilitate
management of workgroups of Mac OS X machines, and to provide access to network services. These tools
include a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others. It is preloaded on Apple's Xserve server hardware, but can be run on almost all of Apple's current selling computer
models.[8]
Apple also produces specialized versions of Mac OS X for use on its consumer devices. iOS, which is
based on Mac OS X, runs on the iPhone, iPod Touch,[9] iPad, and the 2nd generation Apple TV[10]. An
unnamed variant of Mac OS X powered the 1st generation Apple TV.[11]
Mac OS X Version Information
Version
Mac OS X
Codename
Hera
Date Announced Release Date
March 16, 1999
Most Recent Version
1.2v3 (October 27, 2000)
67
Server 1.0
Public Beta
10.0
10.1
10.2
10.3
10.4
10.5
10.6
10.7
Kodiak
Cheetah
Puma
Jaguar
Panther
Tiger
Leopard
Snow Leopard
Lion
September 13, 2000
March 24, 2001
July 18, 2001
September 25, 2001
May 6, 2002
August 24, 2002
June 23, 2003
October 24, 2003
May 4, 2004
April 29, 2005
June 26, 2006
October 26, 2007
June 9, 2008
August 28, 2009
October 20, 2010 Expected Q2 2011
10.0.4 (June 22, 2001)
10.1.5 (June 6, 2002)
10.2.8 (October 3, 2003)
10.3.9 (April 15, 2005)
10.4.11 (November 14, 2007)
10.5.8 (August 5, 2009)
10.6.6 (January 6, 2011)
Linux
Linux (commonly pronounced /ˈlɪnəks/ LIN-əks in American English,[4][5] also pronounced /ˈlɪnʊks/ LIN-ooks[6] in
Europe) refers to the family of Unix-like computer operating systems using the Linux kernel. Linux can be installed
on a wide variety of computer hardware, ranging from mobile phones, tablet computers and video game consoles,
to mainframes and supercomputers.[7][8][9][10] Linux is a leading server operating system, and runs the 10 fastest
supercomputers in the world.[11]
The development of Linux is one of the most prominent examples of free and open source software
collaboration; typically all the underlying source code can be used, freely modified, and redistributed, both
commercially and non-commercially, by anyone under licenses such as the GNU General Public License.
Typically Linux is packaged in a format known as a Linux distribution for desktop and server use. Some
popular mainstream Linux distributions include Debian (and its derivatives such as Ubuntu), Fedora and
openSUSE. Linux distributions include the Linux kernel and supporting utilities and libraries to fulfill the
distribution's intended use.
A distribution oriented toward desktop use may include the X Window System, the GNOME and KDE
Plasma desktop environments. Other distributions may include a less resource intensive desktop such as
LXDE or XFCE for use on older or less-powerful computers. A distribution intended to run as a server may
omit any graphical environment from the standard install and instead include other software such as the
Apache HTTP Server and a SSH server like OpenSSH. Because Linux is freely redistributable, it is
possible for anyone to create a distribution for any intended use. Commonly used applications with desktop
Linux systems include the Mozilla Firefox web-browser, the OpenOffice.org office application suite and
the GIMP image editor.
The name "Linux" comes from the Linux kernel, originally written in 1991 by Linus Torvalds. The main
supporting user space system tools and libraries from the GNU Project (announced in 1983 by Richard
Stallman) are the basis for the Free Software Foundation's preferred name GNU/Linux.[12][13]
Contents

1 History
o 1.1 Unix
o 1.2 GNU
o 1.3 BSD
o 1.4 MINIX
68
o
o
o

1.5 Commercial and popular uptake
1.6 Current development
2 Design
o 2.1 User interface
o

3 Development
o 3.1 Community
o 3.2 Programming on Linux
o

4 Uses
o
o
o
o
o

4.1 Desktop
4.2 Servers, mainframes and supercomputers
4.3 Embedded devices
4.4 Market share and uptake
5 Copyright and naming
o 5.1 GNU/Linux
List of search engines
This is a list of Wikipedia articles about search engines, including web search engines, selection-based
search engines, metasearch engines, desktop search tools, and web portals and vertical market websites that
have a search facility for online databases.
General
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Ask.com (known as Ask Jeeves in the UK)
Baidu (Chinese, Japanese)
Bing (formerly MSN Search and Live Search)
Blekko
Duck Duck Go
Google
Kosmix
Sogou (Chinese)
Yodao (Chinese)
Yahoo
Yandex (Russian)
Yebol
Geographical limited scope
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Accoona, China/US
Alleba, Philippines
Ansearch, Australia/US/UK/NZ
Biglobe, Japan
Daum, Korea
Goo, Japan
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Guruji.com, India
Leit.is, Iceland
Maktoob, Arab World
Onkosh, Arab World
Miner.hu, Hungary
Najdi.si, Slovenia
Naver, Korea
Rambler, Russia
Rediff, India
SAPO, Portugal/Angola/Cabo Verde/Mozambique
Search.ch, Switzerland
Sesam, Norway, Sweden
Seznam, Czech Republic
Walla!, Israel
Yandex, Russia
Yehey!, Philippines
ZipLocal, Canada/US
Accountancy
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IFACnet
Business
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Business.com
GlobalSpec
Nexis (Lexis Nexis)
Thomasnet (United States)
GenieKnows (United States and Canada)
Enterprise
See also: Enterprise search
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AskMeNow: S3 - Semantic Search Solution
Concept Searching Limited: concept search products
Dieselpoint: Search & Navigation
dtSearch: dtSearch Engine (SDK), dtSearch Web
Endeca: Information Access Platform
Exalead: exalead one:enterprise
Expert System S.p.A.: Cogito
Fast Search & Transfer: Enterprise Search Platform (ESP), RetrievalWare (formerly Convera)
Funnelback: Funnelback Search
IBM: OmniFind Enterprise Edition
Inbenta: Inbenta Semantic Search Engine
ISYS Search Software: ISYS:web, ISYS:sdk
Jumper 2.0: Universal search powered by Enterprise bookmarking
Microsoft: SharePoint Search Services
Northern Light
Open Text: Hummingbird Search Server, Livelink Search
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Oracle Corporation: Secure Enterprise Search 10g
SAP: TREX
TeraText: TeraText Suite
Vivisimo: Vivisimo Clustering Engine
X1 Technologies : X1 Enterprise Search
ZyLAB Technologies: ZyIMAGE Information Access Platform
Ethnic

RushmoreDrive (for African Americans)
Mobile/Handheld
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
Taganode Local Search Engine
Taptu: taptu mobile/social search
Job
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Bixee.com (India)
CareerBuilder.com (USA)
Craigslist (by city)
Dice.com (USA)
Eluta.ca (Canada)
Hotjobs.com (USA)
Incruit (Korea)
Indeed.com (USA)
LinkUp.com (USA)
Monster.com (USA), (India)
Naukri.com (India)
Yahoo! HotJobs (Countrywise subdomains, International)
Legal
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WestLaw
Lexis (Lexis Nexis)
Quicklaw
Manupatra
Medical
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Bing Health
Bioinformatic Harvester
EB-eye EMBL-EBI's Search engine
Entrez (includes Pubmed)
GenieKnows
GoPubMed (knowledge-based: GO - GeneOntology and MeSH - Medical Subject Headings)
Healia
Nextbio (Life Science Search Engine)
PubGene
71
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Quertle (Semantic search of the biomedical literature)
Searchmedica
VADLO (Life Sciences Search Engine)
WebMD
News
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Bing News
Google News
Daylife
MagPortal
Newslookup
Nexis (Lexis Nexis)
Topix.net
Yahoo! News
People
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PeekYou
Ex.plode.us
InfoSpace
Spock
Spokeo
Wink
Zabasearch.com
ZoomInfo
Real estate / property
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Fizber.com
Home.co.uk
HotPads.com
Redfin
Rightmove
Zillow.com
Television

TV Genius
Video Games

Wazap (Japan)
By information type
Search engines dedicated to a specific kind of information
72
Forum

Omgili
Blog
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
Amatomu
Bloglines
BlogScope
IceRocket
Technorati
Multimedia
Multimedia search
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
Bing Videos
blinkx
FindSounds
Google Video
Munax's PlayAudioVideo
Picsearch
Pixsta
Podscope
ScienceStage
Songza
SeeqPod
TV Genius
Veveo
TinEye
Yahoo! Video
YouTube
Source code




Google Code Search
JExamples
Koders
Krugle
BitTorrent
These search engines work across the BitTorrent protocol.

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
Btjunkie
FlixFlux
Isohunt
Mininova
The Pirate Bay
TorrentSpy
73
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Torrentz
Email

TEK
Maps
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
Wiki Mapia
Bing Maps
Géoportail
Google Maps
MapQuest
Yahoo! Maps
Price
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
Bing Shopping
Google Product Search (formerly Froogle)
Kelkoo
MySimon
PriceGrabber
PriceRunner
PriceSCAN
Shopping.com
ShopWiki
Shopzilla (also operates Bizrate)
TheFind.com
Wishabi
Question and answer
Human answers



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

Answers.com
eHow
Uclue
Yahoo! Answers
Stack Overflow
DeeperWeb
Timeline
Engine
Year
1993
1994
W3Catalog
Aliweb
JumpStation
WebCrawler
Event
Launch
Launch
Launch
Launch
74
1995
1996
1997
1998
1999
2000
2003
2004
2005
2006
2007
Go.com
Lycos
AltaVista
Daum
Open Text Web Index
Magellan
Excite
SAPO
Yahoo!
Dogpile
Inktomi
HotBot
Ask Jeeves
Northern Light
Yandex
Google
AlltheWeb
GenieKnows
Naver
Teoma
Vivisimo
Baidu
Exalead
Info.com
Yahoo! Search
A9.com
Sogou
MSN Search
Ask.com
GoodSearch
SearchMe
wikiseek
Quaero
Ask.com
Live Search
ChaCha
Guruji.com
wikiseek
Launch
Launch
Launch
Founded
Launch [1]
Launch
Launch
Launch
Launch
Launch
Closed (is not Yahoo!)
Founded
Founded
Launch
Launch
Launch
Launch
Founded
Launch
Founded
Founded
Founded
Founded
Launch
Final launch
Closed
Launch
Closed (is Bing now)
Launch
Launch
Founded
Founded
Founded
Launch
Closed (is now Bing)
Launch
Launch
Closed
75
2008
2009
2010
Sproose
Wikia Search
Blackle.com
Powerset
Picollator
Viewzi
Cuil
Boogami
LeapFish
Forestle
VADLO
Duck Duck Go
Bing
Yebol
Mugurdy
Goby
Yandex global (English)
Cuil
Blekko
Viewzi
Closed
Launched
Launched
Closed (Became Bing)
Closed
Closed
Launched
Launched
Beta Launch
Launched
Launched
Launched
Launched
Beta Launch
Closed due to a lack of funding
Launched
Launched
Closed
Beta Launch
Closed due to a lack of
76