Download IMPORTANCE of computer systems RELIABILITY of computer

OCR GCSE Computing – 2.1.1 (Fundamentals) – REVISION SHEET STANDARD COMPUTER SYSTEM CPU INPUT RELIABILITY of computer systems LEGAL = MUST DO IT ..
How reliable is a computer system?? Data Protection Act Measured by how often it is available – 99% availability..  Personal data‐> Kept secure  Personal data‐> Kept accurate  Personal data‐> Specific Purpose OUTPUT (Processor
Health and safety at work act  Safe working environment  RSI ‐> Keyboards  Posture ‐> Chairs STORAGE Copyright, Designs and Patents Act Computer system – Collection of HARDWARE and SOFTWARE that work together to perform a TASK  Illegal to use software / other media without buying it  Purchasing of licences Mean time before failure (MTBF) If RELIABILITY is essential (Hospital patient monitoring systems) then HARDWARE REDUNDANCY is used to protect system. HARDWARE REDUNDANCY – HAVE MORE THAN ONE CRITICAL COMPONENT SO THEY CAN BE SWAPPED DATA LOSS – Two copies of data stored so data can be restored if necessary – (Previous versions at EMC) Companies using COMPUTERS should have a DISASTER RECOVERY plan – Fire / Flood / Theft …. An effective plan should enable them to get system back online without delay HARDWARE: You can Touch Software : You cannot touch ETHICAL = SHOULD DO IT..
IMPORTANCE of computer systems Environmental 
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Computers are EMBEDDED within many everyday tasks TRAVEL – Traffic Lights / Sat Navs / Flight Control Systems DEVICES – Mobile Phones / Cookers / Microwaves NO COMPUTERS = > Minor inconvenience (Cannot boil kettle) Disposal of old computers Recycling – Give to others Use of landfill Reduce energy – Turn TV off standby / PC off standby / Use SSD drives rather than MAGENTIC Privacy / E‐Netiquette Major safety issues (Traffic lights stop working)  Keep personal details secure  Not post inflammatory / derogatory posts online etc Data Security  Wikileaks – Divulging government secrets – Good or Bad..?? STANDARDS and computer systems Computer systems = complex…. If every company did it their own way they would be even more complex / internet wouldn’t work etc DE FACTO – People/ organisations work certain way and over time this way of working becomes standard – Using INDENTS when coding / Adding comments to programme code. DE JURE – (LAW) Wireless signals – Must be adhered to otherwise different devices will not be able to connect PROPRIETARY –(Owned by organization) Ensure compatibility within companyis products – APPLE AUDIO FORMAT can only be played on APPLE devices INDUSTRY standards‐ Set by industry – IEEE electricians OPEN standards – Collaborative – HTML used to develop web pages / TCPIP used to connect internet LEGAL and ETHICAL – TIP ‐ Think of different areas where computers are used – How are the ETHICAL and LEGAL aspects dealt with – Think of ideas such as installing software – LICENCES…. ROM
RAM READ ONLY MEMORY
RANDOM ACCESS MEMORY (Main memory) Start Up programme – BOOT PROGRAMME (BIOS) NON VOLATILE Not easily deleted / Changed Store programmes AND data that computer is working on VOLATILE Can be changed More RAM = Faster processing Size 4Gb upwards OCR GCSE Computing – 2.1.2 (Hardware) – REVISION SHEET FETCH Instruction / Data Hardware EXECUTE the INSTRUCTION CPU + ‐ x ÷ Hardware Size : 1 or 2 Mb BOOT Performs basic checks Finds operating system ‐> RAM Hands over control ‐> Op System
DECODE the INSTRUCTION Virtual Memory = Extension of RAM ‐ > Computer runs out of RAM will stop Swapping of programs from RAM to Virtual memory will slow computer PERFORMANCE Cache Memory – Located on processor ‐ > Buffer between processor (FAST FAST Clock speed = time to perform 1 CYCLE = 1 Hz FAST) and Memory (Slow..) CPU = Fast Memory = Slow ‐> Bottleneck Flash memory – Special type of RAM that is NON‐ VOLATILE (Does not need Add faster memory – Increase Cost ‐ > ££££££££££ continual power supply). Cannot replace RAM as read/write is SLOW Cache memory – Stores frequently used instructions – Much faster ‐ > Reduces bottleneck Uses : Memory Cards / Smartphones / USB Sticks / Solid State Drives(SSD) MEMORY TECHNOLOGY Cache memory = £££££££ so use small amount STORAGE ‐ > Portability 1 Core = 1 Processor – Multiple cores = Multiple Processors so Multiple cycles ACCESS ‐ > Fast read/write times – Performance goes up LESS POWER ‐ > Battery life increases LOWER COSTS INPUT DEVICE
STORAGE DEVICE OUTPUT DEVICE
Keyboard Mouse Touch Screen Barcode Scanner OMR (Lottery / Multiple choice) Joystick Microphone Sensors Optical ‐ CD / DVD Magnetic Hard Drive Solid State Monitor Speakers Headphones Printer SELECT
SELECT
SELECT
Supermarket School House for disabled person Patient Monitoring CAPACITY SPEED PORTABLE DURABILITY RELIABILITY Supermarket School House for disabled person Patient Monitoring OCR GCSE Computing – 2.1.3 (SOFTWARE) – REVISION SHEET Software SYSTEM SOFTWARE ‐ OPERATING SYSTEMS (OS) – (LEARN 5 features)
Group of programmes that manages system resources. Any program that runs on a computer 1) MEMORY MANAGEMENT – When programme is running it is stored in computers memory. OS must manage where it goes. (LINK to hardware section – See Fetch Execute Cycle – When instruction is needed the OS will load it from main memory) 2) MULTI‐TASKING / PROCESS MANAGEMENT – Single Core processor can only execute ONE instruction at a time. Some programmes are more URGENT than others so have a higher priority. SYSTEM SOFTWARE Programs used to OPERATE and MAINTAIN the computer such as the OPERATING SYSTEM APPICATIONS SOFTWARE Programs that PERFORM a TASK for the USER e.g. Wordprocessor (Process – What we call a programme when it is RUNNING in main memory of computer) 3) PERIPHERAL MANAGEMENT – OS must manage all the INPUT DEVICES, STORAGE DEVICES and OUTPUT DEVICES. When a key is pressed the OS ensures that the KEY PRESS recognized on the keyboard and sent to the CPU APPLICATION SOFTWARE Group of software that PERFORMS a SPECIFIC task for the USER OPEN SOURCE (Peripeheral – Any piece of computer hardware that is not part of CPU) PROPRIETARY Licensed but NO CHARGE – Anyone can use Software sold with LICENSE – Costs money Restrictions – Users or machines Programme code is available Any new software created must be OPEN SOURCE as well Programme code not available New software can be sold on and money made ADV – No cost DIS – Lack of support / Stability / Backup ADV – Support / OnLine training / Updates DIS – Expensive / Hacking targets 4) SECURITY – Restrict access to machine and/or files.. Allow setting of parental controls for access 5) USER INTERFACE – The way that we interact with the computer.. Interfaces can use Windows, Icons, Menus, Pointers (WIMP) or touch systems such as on phones UTILITY PROGRAMMES – (Learn some examples) Not essential but provide HOUSEKEEPING tools ANTI VIRUS CUSTOM WRITTEN Written for a customer for their SPECIFIC requirements OFF THE SHELF Go into a shop / online and BUY IT
Pay development costs Takes time before it can be used Don’t pay development costs Available immediately Programs used to OPERATE and MAINTAIN the computer such as the OPERATING SYSTEM FIREWALL Blocks access from the internet to a PC / Network, Restricts web access Disk Defragmenter One programme will be stored on a disk in different places. Disk Defragmenter rearranges files so they are next to each other making reading files more quicker. Others – SYSTEM INFORMATION / SYSTEM CLEANUP / AUTOMATIC UPDATING Adv – No Features that you will not use / Easy Adv – Available straight away / Cheaper than to use / Specific to task custom written / Plenty of support Regular Updates Dis – NOT available straight away / More Dis – Features that you will not use / expensive than off the shelf / Not much support / Updates only when you spot errorss Complicated / Not specific to task KEY TERMS TIP – Look for patterns when learning the advantages and disadvantages – THINK of the following aspects: COST SPECIFIC to task AVAILABILITY SUPPORT / TRAINING SOFTWARE
SYSTEM Software
Operating System
Utility Programmes
APPLICATION Software
Translators
Off The shelf
Custom Written
Open Source
Proprietary
CONVERSIONS
OCR GCSE Computing – 2.1.4 (REPRESENTING DATA) – REVISION SHEET Understand HOW to convert from BINARY HEXADECIMAL BINARY REPRESENTING DATA IN COMPUTERS DENARY (Normal eg 68) Data can be stored in different format such as NUMBERS, TEXT, SOUNDS, IMAGES and PROGRAM COMMANDS B B
NIBBLE = 4 BINARY DIGITS ELECTRIC CIRCUITS and BINARY Computers consist of circuits that either allow electricity to flow (1) or not (0). Single 1 or 0 = Binary Digit (BIT) 4 BITS = 1 NIBBLE 8 BITS = 1 BYTE 1024 BYTES = 1 KILOBYTE 1024 KILOBYTES = 1 MEGABYTE 1024 MEGABYTES= 1 GIGABYTE 1024 GIGABYTES= 1 TERABYTE TIP – LEARN BYTE / KILO / MEGA / GIGA / TERA and then remember that we multiply by 1024 1) Write out binary headings 128/64/32 etc HEXADECMIAL uses 0,1,2,3,4,5,6,7,8,9, A, B, C, D,E, F where A=10, B=11 etc
2) Add up the value of each DIGIT
DENARY to HEXADECIMAL CONVERT DENARY to BINARY and then convert this to HEXADECIMAL e.g. 70 = 0100 0110 in Binary which is 4 6 in HEXADECIMAL HEXADECIMAL to DENARY CONVERT HEXADECIMAL to BINARY and then BINARY to DECIMAL e.g. 7E Binary = 0111 1110 in Binary which is 64 + 32 + 16 + 8 + 4 + 2 = 126 in denary REPRESENTING SOUND SOUND is CONTINUALLY CHANGING so is SAMPLED at intervals called SAMPLE INTERVAL. Number of BITS used to store value is SAMPLE RESOULTION – The higher each of these is the BETTER QUALITY the sound is SOUND WAVE
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1 2 3 4 5 6 7 8 9 10 11 12 0.8 2 3.4 5 6.6 8.1 10 12 14 16 17.4 18 REPRESENTING CHARACTERS
REPRESENTING IMAGES KEY PRESSED ‐> Code transmitted to computer ‐>Code is stored as BINARY PC’s use ASCII codes The characters that can be represented is called a character set Making an IMAGE file: Image uses four colours – To store we would save 10 10 10 etc… If we use 8 bits i.e. 0000 0000 to 11111111 we can represent up to 255 characters as 1111 1111 represents 255 in denary 5
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
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10 00 10 00 10 00 10 10 11 10 10 10 00 00 00 10 10 10 11 11 10 10 00 00 01 00 00 10 10 11 11 10 10 10 00 00 00 11 11 10 10 11 11 10 00 10 00 10 00 10 11 11 11 10 10 10 10 10 10 10 10 11 10 10 10 10 10 10 10 10 10 10 10 10 10 11 10 01 00
Using TWO BITS per pixel we can use 4 colours… Using FOUR BITS per pixel we can use 15 colours Number of bits used for each pixel is the colour depth If the image is stored as 10 10 10 10 10 10 10 10 10 00…. Then to make the image the computer needs to know the COLOUR DEPTH, THE IMAGE HEIGHT and the IMAGE WIDTH
OCR GCSE Computing – 2.1.5 (Database) – REVISION SHEET DATABASE = DATABASE TERMS PERSISTENT Structure Maintained when programmes not running (NON VALATILE) RECORD ORGANISED Records / Fields FIELD STORE OF DATA PRIMARY KEY Sales Accounts Training Sales File
Accounts File
Training File
Sales RELATIONSHIP QUERY Accounts
Training
Company Database
FORM REPORT DBMS ‐ > MANAGE MODULE SECURITY Sales
INTEGRITY QUERYING Database DBMS
LOGS Sales
VALIDATION Key Fields to CONNECT Databases ENTITY – REAL WORLS THING about which data is held A CUSTOMER, A DVD, A CAR, A TREATMENT etc ATTRIBUTE = FEATURE OF THAT ENTITY ENTITY stored as TABLE, ATTRIBUTE stored as FIELD VALIDATION
Rule built into database to check that the data entered is Sensible Complete Reasonable Within Boundaries Methods of Validation Type Checks Length Checks Range Checks Lookup Check Digits Input Masks Presence Checks Sales
SEPERATION
OCR GCSE Computing – 2.1.5 (Database) – REVISION SHEET FORM QUERY REPORT A complex query looks for data in two or more fields and uses the logical operators OR, AND or NOT. The following example uses a complex query to find all of the pupils in Form 10B who were born before 1995. This query uses the logical operator AND: (Form = “10B”) AND (Date of Birth < 01/01/1995). OCR GCSE Computing – 2.1.6 (Networks) – REVISION SHEET NETWORK TOPOLOGIES – How Computers are connected in a network LAN = LOCAL AREA NETWORK A collection of computers and devices connected together within a SINGLE SITE WAN = WIDE AREA NETWORK A collection of computers and devices that are NOT PHYSICALLY CONNECTED by computers but use other INFRASTRUCTURE such as the internet Benefits of networking Sharing FILES and FOLDERS SHARING Sharing PRINTERS and other devices SHARING Sharing INTERNET connection SHARING Use email to communicate COMMUNICATION Instant messaging COMUNICTATION Security managed centrally MANAGEMMENT Software distributed via network MANAGEMENT All PC’s have cable connected them to central PC (Server) Advantages
Disadvantages
One cable breaks Costly to install –
only 1 station breaks Need powerful server Consistent Dependance on performace central computer Easy to add new PCs
Computers connected to single backbone cable. This is ahred. Only one computer can transmit at a time Advantages Disadvantages
Easy to install Main cable breaks whole network breaks Less Cabling Low performance if network busy East to add new PCs
Computers connected to adjacent computers in a RING. Computers take it in turns to transmit passing a TOKEN around Advantages
Disadvantages
Not dependant on Single PC or cable central computer breaks whole network breaks Simple and Reliable
Consistent performance even when network is busy NETWORK SECURITY CLIENT SERVER vs PEER TO PEER IP / MAC / PACKETS / PROTOCOLS
When we go aborad its hard to communicate as we are using different languages ‐ > i.e we are using different protocols. If we speak French in France then we are using the SAME PROTOCOLS. PROTOLCOLS = RULES OF COMMUNICATION INTERNET PROTOCOL (IP address) Each device on the INTERNET has its own IP ADDRESS which is a series of 4 numbers separated by dots i.e. 193 . 127 . 030 . 023 PEER TO PEER All PCs have equal status Easy to set up & maintain No centralised management Backup each computer seperatly Not depdendant on a server CLIENT SERVER Needs network manager Backup done centrally Centralised security Shared resources MAC ADDRESS Each network card has its own MAC ADDRESS which is like its postyal address. Its used to transmit signals between devices on a LAN. PACKETS In a communication one device will send a message to another. The message will be broken down into PACKETS. Each packet will then be broadcast with the MAC address of the destination. At the other end the device will listen for signals and will recognize the MAC NETWORK SECURITY MEASURES 1) PREVENTATIVE AIM – Stop hazards occurring Access rights – Only allow to see what they need to see Firewalls – Prevent nasties from coming onto PC Passwords – Stop unauthorized people accessing network 2) DETECTIVE Detecting when data has been corrupted / hacked Virus Checking software Fire Alarms / Access alarms Audit trails – Recording when data is changed and by whom 3) CORRECTIVE Backup and Restore Redundant hardware / Failover Disaster recovery procedures Network Policies Security Precautions ACCESS RIGHTS Backup & Restore ENCRYPTION Archiving PASSWORD PROTECTION Disaster Recovery Failover AUP OCR GCSE Computing – 2.1.6 (Networks) – REVISION SHEET HTML and CSS
INTERNET = WAN (Wide area network)
The INTERNET is a world wide collection of computers that uses the INTERNET PROTOCOL to communicate. NETWORK is made up of network devices called ROUTERS. HTML – Programming language used to create WEB PAGES for the WWW HTML is the STANDARD web programming languages – All web pages have their main content set up in this way. All web pages will have the following structure: <html> <head> <Title> Web page example </title> </head> <body> MAIN BODY OF WEB PAGE GOES HERE </body> ADVANTAGES Web pages on different servers and different types of network are ALL set up in the same way People can create webpages knowing what they will look like Browsers can receive the web page and display it correctly. IP ADDRESS Each device has a unique IP ADDRESS. Websites are stored on WEB SERVERS which are connected to the INTERNET. Accessing Websites 1. User types in a web address e.g. www.bbc.co.uk 2. Web address translated to IP address by a DNS (Domain name System) server which has a database of Web addresses and their IP Addresses. If DNS doesn’t have IP address links with other DNS servers 3. PC sends request for webpage 4. Web Server then sends web page back using PACKETS COMPRESSING IMAGES Use fewer bits per pixel – JPEG uses 24bits per pixel giving a high quality image, GIF uses 8 bits per pixel so is lower quality – You will see solid blocks rather than gradual tones FILE TYPES and FILE COMPRESSION HTML – Programming language used to create WEB PAGES for the WWW When data is transmitted across the internet it will go through many different links between routers. The connection from your PC to the internet will be the slowest. If we makes the files being transmitted smaller then they will move across the interent quicker LOSSY COMPRESSION Files are compressed by REMOVING some of the DETAIL e.g Store photographs using 4 bits for the colour rather than 8 BITS ‐> This will use less colours so the image will not be as sharp. Audio files can be compressed by removing the sounds that humans cannot here. LOSSLESS COMPRESSION Files are compressed but NO DATA IS LOST. COMPRESSING VIDEOS Video files are mostly stored as MPEG format: MPEG 1 – Low resolution videos on a website (10 frames per second) MPEG 2 – Higher Resolution MPEG 4 – High quality broadcast video (24 frames per second) Lower quality uses a lower FRAME RATE HARDWARE needed to connect MODEM Cheapest but SLOWEST tyoe of connection – Uses telephone system LOCAL ROUTER Usually WIRELESS so multiple devices can connect to the internet. COMPRESSING SOUND Video files are mostly stored as MPEG format: MP3 – Music downloads – Deletes part of sound that we cannot here WAV files – Higher quality used to manipulate sound files and to construct music DOCUMENT FILE TYPES Documents created in wide variety of packages with each having their own format – WORD (DOC) PUBLISHER (PUB) POWERPOINT (PPT) When SHARING documents this means recipient needs the software that was used to create it. PDF (Portable document format) eliminates this as documents can be saved in PDF format, these can be sent to other people and FREE READERS are available that lets them view the document. When saving in PDF files you can REDUCE the file size by compressing OCR GCSE Computing – 2.1.7 (Programming) – REVISION SHEET
FLOWCHARTS
INPUT HANDLING DATA of Algorithms
CONTROL FLOW
Integer = whole number, positive or negative
Sequence Real = numbers with a decimal or fractional part
 The path a program follows
 Instructions carried out in order Selection
 IF...THEN...ELSE
 IF..THEN...ELSE IF...ELSE
 CASE ANSWER = X: OUTPUT= Y
STORAGE STANDARD SETS OF SHAPES USED TO DEFINE ACTIONS TO BE USED TO SOLVE A PROBLEM
Iteration
 Count-controlled loop (For..Next)
 Condition-controlled loop
(Repeat ...Until / While...EndWhile)
Character = single alphanumeric character
String = a number of alphanumeric characters put together
Boolean = TRUE or FALSE
Variable = named store in a program that can vary over time
Constant = named store in a program that is a fixed value
MOD = Modulus or the remainder of a division sum
DIV = Quotient or the main result of a division sum
Array = a set of variables collected together with the same identifier
Operator Priority = order that operators carried out - BIDMAS
PROGRAMMING LANGUAGES
PSEUDOCODE
Structured form of English used to describe flowcharts for i = 0 =to 7
print("Hello") next i
if entry == "a" then
print ("Hello")
elseif entry == "b" then ,etc..
MACHINE CODE - low-level code
 Software provided to processor using it
 Stream of binary bit instructions
 Decoded by logic circuits and executed
 Difficult and time consuming
ASSEMBLY - low-level language
 Opcode and Operand
 1st set of bits is code, next is data
PROGRAMMING LANGUAGES - high-level  Can action several commands in 1 line
. Compiler converts work to machine code
. Interpreter converts code to instruction
. Translator helps write it (IDE)
TESTING Ensure systems function correctly and as required
SYNTAX ERRORS – Rules of language broken i.e. variables not declared,
or spelt incorrectly, etc.
LOGIC ERRORS – Structure of program leads to unexpected results, i.e.
infinite looping program filling memory, division by zero, etc.
NORMAL TEST DATA – Data that is expected to be input into a system
BOUNDARY / EXTREME TEST DATA - Data either side of a boundary limit
i.e. -1,0,1
ERRONEOUS TEST DATA - Data that is a completely different data type
than expected, i.e. numbers is a text cell