Download Promotion Test - Computer Notes

Generations of computers
First Generation (1940-56)
Used vacuum tubes for memory & machine language for giving instructions.
Input was based on punched cards & paper tape, output was displayed on printouts
Second Generation (1956-63)
Vacuum tubes replaced by transistors.
Moved from the use of machine language to assembly language.
Third Generation (1964-71)
Computers were built using integrated circuits (IC)
Keyboards & monitors were used instead of punched cards.
Fourth Generation (1971-90)
Computers used microprocessor chips.
In microprocessor thousands of integrated circuits were built into a single silicon
chip.
VLSI (Very large Scale Integration) technology used.
Fifth Generation – Present & Beyond
Based on artificial intelligence, are still in their developmental stage.
ULSI technology used (Ultra Large Scale Integration).
Computer system has two major components – hardware & software.
Hardware refers to all the physical items associated with a computer system.
Software is a set of instructions, which enables the hardware to perform a specific
task.
Input devices allow the user to enter the program & data & send it to the
processing unit.
eg :- keyboard, mouse & scanner.
Output devices
The result produced by the CPU is in the form of electronic binary signals.
It has to be converted which can be understood by human beings. This function is
performed by output devices.
eg :- monitor, printer, speakers, projector.
Computer
A computer has four functions.
Input
accepts data
Processing
processes data
Output
produces output
Storage
stores result
Input
Input is the raw information entered into a computer from the input devices.
Process
Process is the operation of data as per given instruction.
Output
Output is the processed data given by computer after data processing. Output is
also called as Result.
Computer system
All of the components of a computer system can be summarized with the equation:
Computer system = Hardware + Software + User.
Hardware
All physical parts of a computer (or everything that we can touch) are known as
hardware.
Hardware = Internal devices + Peripheral devices.
eg :- keyboard, mouse, hard disk etc.
Software
Software is a set of instructions, which enables the hardware to perform a specific
task. Software can be classified as:
a) System software
b) Application software
System Software
System software consists of several programs, which are directly responsible for
controlling, integrating & managing the individual hardware components of a
computer system. It also provides the interface between the user & component of a
computer.
Application Software
It is a software used to run a particular application on the computer system or
perform a specific task.
eg :- Tally, MS-Word
System software can further be divided into:
1) System management program
2) Developing software
Some common examples of system management programs are operating systems,
device driver & system utilities.
Operating System
It consists of programs, which controls, co-ordinates & supervises the activities of
various components of a computer system. Its function is to provide link between
the computer hardware & user.
eg :- MS-DOS, Windows 7, Linux etc.
Device drivers
A software which is written with the objective of making a device functional when
it is connected to the computer is called driver. Every device, whether it is a
printer, monitor or keyboard has a driver program monitor or keyboard has a driver
program associated with it for its proper functioning.
System utilities
These programs perform tasks related to the maintenance of the computer system.
eg :- Antivirus, disk cleaners, backup utilities etc.
Developing software
It is software which provides service required for the development & execution of
application software.
Programming language
A programming language is a primary interface of a programmer with a computer.
Programming languages are divided into two categories.
1) Low Level Languages
2) High Level Languages
Low Level Languages (LLL)
Divided into two types.
a) Machine language
b) Assembly language
a) Machine language
It is uses two binary digits 0 & 1. It is directly understood by the computer. It is
referred to as machine code or object code. This language was used by
programmers in First Generation of Computers.
b) Assembly language
It is used to provide an interface with computer hardware. It is not understood by
the computer. So a translator known as assembler is needed to convert assembly
language was used in Second Generation of Computers.
High Level Languages (HLL)
It is a machine independent language & uses translator. It is also called source
code.
Language translator
A language translator helps in converting programming languages to machine
language. The translated program is called the object code. These are three types of
language translators.
Assembler
It is used to convert the assembly language into machine language consists of
mnemonic codes which are difficult to learn and is machine dependent.
Compiler
It is used to convert the source code (Written in high level language) into machine
language.
Interpreter
This language processor converts a high-level language program into machine
language by converting it line-by-line. It is useful while finding errors in a
program.
Input and output devices
A computer interacts with the external environment via the Input – output devices
attached to it.
Input device is used for providing data and instructions to the computer. After
processing the input to the user via the output devices.
Input devices
Keyboard, mouse, light pen, scanner, microphone, trackball, joy stick, barcode
reader, web camera.
Keyboard
Keyboard is the most common input device. Generally standard keyboard has 104
keys. Arranged into six groups.
(i) Alphanumeric keys
The letters are arranged as in a typewriter & the arrangement is called QWERTY.
(ii) Modifier keys
They are used to modify the input of other keys. The modifier keys are Shift, Ctrl
and Alt.
(iii) Numeric keypad
Usually located at the right side of the keyboard & is similar to a calculator.
Numeric keypad also has a Num Lock key which forces the key in the numeric
keypad to output numbers.
(iv) Function keys
The function keys (F1 to F12) are usually arranged at the top of the keyboard in a
single row. They allow you to input commands without typing the commands. The
commands vary according to different softwares.
(v) Cursor Movement keys
Special keys on keyboard that move the cursor. The arrow keys, for example,
move the cursor up, down, right & left. In addition there is Home, End, Page up,
Page down & Backspace keys.
(vi) Special purpose keys
Some keys in the keyboard has specific functions.
Tab
: Move between items or move forward five characters.
Shift
: When a shift key is pressed at the same letter, an upper case version of
that letter is produced.
Alt Gr : Used on international keyboards to access special characters on keys.
Where there are more than two characters on the key.
Ctrl
: Holding down the control key while selecting items allows you to select
several items at once. The Ctrl key is also used in many keyboard shortcuts.
Print Screen : Pressing the print screen key captures an image of your entire
screen.
Caps Lock
: To type upper case letters continuously with having to press the
Shift key at the same time.
Scroll Lock : When the scroll lock mode is on, the arrow keys would scroll the
contents of a text window instead of moving a cursor.
Shortcut keys
Ctrl. X – cut
Ctrl. N – new file
Ctrl. C – copy
Ctrl. P – print
Ctrl. S – save
Ctrl. B – bold
Ctrl. V – paste
Ctrl. I – italics
Ctrl. Z – undo
Ctrl. U – underline
Ctrl. Y – redo
Ctrl. A – select all text
Shift + Del – delete files permanently
Ctrl + Esc – bring up start menu
Ctrl + K
- create a hyperlink
Alt + F4 - closes current open program
Ctrl+ Alt+ Del- close an application or turn off your computer
Alt + Tab – change between windows that are open on the desktop
Alt + Enter – opens windows Task Manager
Home
- goes to the beginning of current line
End
- goes to the end of current line
Ctrl + End - goes to the end of document
Ctrl+ Home- goes to the beginning of document
F1
-
help
F2
-
rename a selected file
F3
-
search
F4
-
open the address bar in I Explorer
F5
-
refresh
F6
-
move the cursor to the address bar in browser
F7
-
spell check a document in MS-Word
F8
-
windows startup menu
F9
-
send or receive mail in Microsoft outlook, refresh document
MS-Word
F10
-
activate the menu bar of an open application
F11
-
enter & exit mode in all modern internet browsers
F12
-
open the ‘save as’ window in MS-Word
in
Mouse
Mouse is a pointing device invented by Douglas Engel Bart. It may be used to
position the cursor on the screen, move an object by dragging or select an object by
clicking.
Light Pen
An input device that utilizes a light-sensitive detector to select objects on a display
screen.
Trackball
An alternative to mouse, a trackball can be placed on any surface, it is stationary &
does not require much space to use it.
Joystick
Graphical pointing device, primarily used in video games & controlling robots etc.
Barcode reader
An input device used for reading printing barcodes.
Microphone
Microphone converts the received sound into computer’s format called digital
audio with the help of sound card.
Web Camera
Digital camera attached to the computers & can be used for video conferencing or
online chatting.
Scanner
Scanner is a light-sensing input device that converts printed text & graphics into
digital form that can be further processed by the computer.
Two popular types of scanners are:1) Flatbed Scanner
Works like a copy machine except that it creates a file of the document rather than
a paper copy.
2) Handheld Scanner
Can be manually passed over the image to be scanned ideal for capturing small
images, such as signatures & logos.
Monitors
Monitor is the most commonly used output device, also called as Visual Display
Unit (VDU).
Various types of computer monitor:CRT
-
Cathode Ray Tube
TFT
-
Thin Film Transistor
LCD
-
Liquid Crystal Display
LED
-
Light Emitting Diode
Resolution is the image quality displayed on a monitor. The resolution is measured
by the number of pixels (Picture Elements). Most common resolution is 1024 x
768 pixels. The size of a monitor is usually described by the length of its diagonal,
which is the distance between opposite corners, usually in inches.
Printer
Printers are classified into Impact printers & Non-Impact printers.
Impact printers
Printers that work by banging a head or needle against ink ribbon to make a mark
on the paper.
eg:- Dot-matrix printers, daisy wheel printers, line printers.
Tally T2250 (24 Pins)
Epson LX- 300 (9 Pins)
Dot – Matrix Printer
Epson LQ – 2090 (24 Pins)
Non–Impact Printer
A Printer that prints without banging a ribbon onto paper.
eg: Laser Printer.
Speed of a printer measured in character per second (CPS)
Lines per Minute (LPM) &
Pages per Minute (PPM)
Plotter
It is a computer printer for printing graphical images.
Input devices
Output
Both input & Output
Keyboard
Printer
Modem
Mouse
Monitor
Touch Screen
Light Pen
Plotter
Fax
Scanner
Speaker
Soundcard
Trackball
Projector
Microphone
Joystick
Web camera
Bar code reader
Central Processing Unit (CPU)
CPU is often called the brain of Computer. The CPU is also known as the input
and output devices and performs arithmetic and logic operations specified by the
user.
Arithmetic and Logic Unit (ALU)
Performs all Arithmetic calculations (addition, subtraction, division and
multiplication) & logical calculation includes comparison, greater than, less than
etc,. ALU gives computer the decision making capabilities Actual data processing
is done by ALU.
Control Unit
Control unit co-ordinates the input and output devices of a computer. It organizes
the processing of data into information.
Memory Unit
Memory is that part of the computer, which holds data.
Primary Memory
Primary Memory or main memory of the computer is used to store the data and
instructions during execution of the instructions Primary Memory of two types:
1) RAM (Random Access Memory)
2) ROM (Read Only Memory)
RAM
RAM is also known as read/write memory that allows CPU to read as well as write
data and instructions into it. It is temporary and volatile in nature, when the power
is turned off, the contents of the RAM are lost forever. They are of two types:
a) Dynamic RAM (DRAM)
b) Static RAM (SRAM)
a) DRAM
Slower, less expensive and occupies less space on the computers motherboard.
b) SRAM
Often it is used as cache memory due to its high speed. SRAM is more expensive
than DRAM.
2) ROM
ROM is known as non-volatile memory or permanent storage. It does not lose its
content when the power is switched off. ROM has only read capability, no write
capability. ROM can have data and instructions written to it only one time. The
instructions stored in RAM are often called a firmware. There are 3 types of ROM:
(a) Programmable ROM (PROM)
(b) Erasable programmable ROM (EPROM)
(C) Electrically Erasable Programmable ROM (EEPROM)
a)PROM
Once a PROM has been programmed, its contents can never be changed. It is a
one –time programmable device. PROM generally found in mobile phones, video
game consoles and implantable medical devices.
(b)EPROM
can be erased by using strong UV light, then rewritten.
It
(c)EEPROM
can be programmed several times, but can be erased by using electrical signals.
It
Secondary Memory
Stores much
larger amounts of data and information for extended period of time. It is a non
volatile. Examples are hard disk, floppy disk, CD- ROM, DVD, pen drive.
DVD – Digital Versatile Disk.
CD- ROM – Compact Disk Read Only Memory.
Pen Drive
It is also known as flash drive. It is a storage device that consists of flash memory
(key memory) with a portable USB (Universal Serial Bus) interface.
Memory Measurement
Bit is the smallest memory measurement unit. It is the individual unit of memory
which is either 0 or 1.
Nibble
:
a group of four bits.
Byte
:
a group of 8 bits.
Word
:
a group of 16 bits.
Kilobyte
:
a group of 1024 bytes.
(KB)
1 Bit
8 bits
=
=
Binary Digit
1 Byte
1024 bytes
=
1 KB (Kilo Byte)
1024 KB
=
1 MB (Mega Byte)
1024 M B
=
1 GB (Giga Byte)
1024 GB
=
1 TB (Terra Byte)
1024 TB
=
1 PB (Peta Byte)
Geop Byte is the highest memory measurement unit.
Data Representation Codes used in Computers
1) ASCII - (American Standard Code for Information Interchange)
Unique code is given to each key on the keyboard. ASCII characters are
represented by seven bits.
ASCII code for A-Z – 65-90
ASCII code for a-z – 97- 122
2) BCD - (Binary Coded Decimal)
BCD numbers express each decimal digit as Nibble. It means four bits are used to
represent each decimal digit.
3) EBCDIC (Extended Binary Coded Decimal Interchange Code)
Characters are represented by 8 bits.
4) UNICODE
It uses 16 bits to represent a symbol in the data. It represents any non-English
character, scientific symbol in any language like Chinese, Japanese etc.
Types of computer network
A computer network is a collection of two or more computers, which are
connected together to share information and resources. User’s computer is a
workstation on the network. The world’s largest computer network is the internet.
1) Personal Area Network (PAN)
It is used for communication among various electronic devices such as
Personal computers, mobile phones in close proximity etc.
eg. Bluetooth, Wireless USB.
2) Local Area Network
It connects computers and devices located close to one another, such
As in one building. Here all the terminals are connected to a main
Computer called server.
eg. Networks within schools, college, office building etc.
3) Wide Area Network
It uses telephone lines, satellite links and other long-range Communication
technologies to connect. The networks that make up a
WAN may be located throughout a country or even around the world.
Largest WAN – Internet
4) Metropolitan Area Network (MAN)
It is a collection of LAN. It is a data network designed for a town or city.
It connects an area larger than a LAN but smaller than a WAN.
eg. Cable TV network, branches of a local bank in a city.
Network devices
Repeaters
It have two parts and can connect two segments of a LAN. It amplifies the feabile
signals when they are transported over a long distance so that the signal can be as
strong as the original signal.
Hub
Hub is like a repeater with multiple parts used to connect the network channels. It
acts as a centralized connection to several computers with the central mode or
server.
Switch
It is a hardware device which joins multiple computers together within one LAN. It
helps to reduce overall network traffic.
Bridge
Bridge filters data traffic at a network boundary.
Router
Router is a hardware device which is designed to receive, analyze and convert the
packet data with two or more networks.
Network Interface Card (NIC)
It is a device that connects a computer to a computer network.
RJ II Connector
RJ- Registered Jack.
It establishes a bridged connection for one telephone line.
RJ 45 Connector
It is used to connect computers onto a LAN.
Bandwidth
It means the data transfer rate. It is measured in Cycles per second (CPS) usually
called Hertz (Hz).
IP address
It stands for Internet Protocol Address. It is a 32 bit, four part address separated by
dots.
192.168.0.1.
It is a unique address which identifies a computer in the network.
Network Topology
The art of connecting different computers in a network is known as topology.
Bus Topology
All the nodes are connected to a central cable called bus. All the nodes are
connected directly. So very short cable length is required.
Ring or Circular Topology
Computers are connected in the shape of a closed ring. Data travels only in one
direction. Each computer passes the data to the next one on the line automatically.
Star Topology
All the nodes are connected to a central computer called server. The switch
controls all the communication on the network.
Protocol
Set of rules used by a network for communication.
Internet Protocol
Protocol by which data is send from one computer to another on the internet.
Hyper Text Transfer Protocol (HTTP)
Set of rules for transferring files (text, sound, images, video etc.,) on the WWW.
Cache Memory
A high speed memory placed in between RAM & CPU. It increases the speed of
processing, cache memory is very expensive, so it is smaller in size. It is a
temporary storage that stores the data that is used more often and makes them
available to CPU at a fast rate. The technique of transferring a copy of data from
main memory to a cache memory is called mapping.
Buffer
a temporary physical storage used to hold data during execution of process from
one place to another.
Bus
All the components in the motherboard can communicate with each other with the
help of the communication channels called as buses.
A bus is a set of wires used for interconnection, where each wire can carry one bit
of data.
A computer bus can be divided into two types.
Internal Bus
Internal bus connects components inside the motherboard like CPU and system
memory also called as system bus.
External bus
connects the different external devices, peripherals, expansion slots, 1/0 parts and
drive connections to the rest of computer also called as expansion bus.
Motherboard
main circuit board in a computer also known as system board or main board
also known as the backbone of computer.
SWITCHING TECHNIQUES
Switching techniques are used for transmitting data across networks.
Different types are :
 Circuit Switching
 Message Switching
 Packet Switching
Circuit Switching
 Circuit Switching is the transmission technology that has been used since the
first communication networks in the nineteenth century.
 First the complete physical connection between two computers is established
and then the data are transmitted from the source computer to the
destination.
 When a call is placed the switching equipment within the system seeks out a
physical copper path all the way from the sender to the receiver.
 It is must to setup an end-to-end connection between computers before any
data can be sent.
 The circuit is terminated when the connection is closed.
 In circuit switching, resources remain allocated during the full length of a
communication, after a circuit is established and until the circuit is
terminated and the allocated resources are freed.
Message Switching
 In this the source computer sends data or the message to the switching
circuit which stores the data in its buffer.
 Then using any free link to the switching circuit the data is send to the
switching circuit.
 Entire message is sent to the destination. It reaches through different
intermediate nodes following the “store and forward” approach.
 No dedicated connection is required.
Packet Switching
 Conceived in the 1960’s, packet switching is a more recent technology than
circuit switching.
 Packet switching introduces the idea of cutting data i.e. at the source entire
message is broken in smaller pieces called packets which are transmitted
over a network without any resource being allocated.
 Then each packet is transmitted and each packet may follow any rout
available and at destination packets may reach in random order.
 If no data is available at the sender at some point during a communication,
then no packet is transmitted over the network and no resources are wasted.
 At the destination when all packets are received they are merged to form the
original message.
 In packet switching all the packets of fixed size are stored in main memory.
DATA COMMUNICATION TERMINOLOGIES
Data channel
Baud & bits per second (bps)
 The information / data carry from one
end to another in the network by
channel.
 It’s used to measurement for the
information carry of a communication
channel.
 Measurement Units : bit
 1 Byte = 8 bits
 1 KBPS (Kilo Byte Per Second) =


Bandwidth


1024 Bytes.
1 kbps (kilobits Per Second) = 1024
bits.
1 Mbps (Mega bits per second)= 1024
Kbps
It is amount of information transmitted
or receives per unit time.
It is measuring in Kbps/Mbps etc unit.
Transmission Media
 data is transmitted over copper wires, fiber optic cable, radio and
microwaves. The term ‘media’ is used to generically refer to the physical
connectors, wires or devices used to plug things together.
 Basic communications media types
 copper
o unshielded twisted pair (utp)
o shielded twisted pair (stp)
o coaxial cable (thinnet, thicknet)
 fiber optic
o single-mode
o multi-mode
 infrared
 radio & microwave
Twisted Pair Cable

These cables consist of two insulated copper wires twisted around each
other in a double helix.
 Twisting of wires reduces crosstalk which is bleeding of a signal from one
wire to another.
Types :
 Unshielded Twisted Pair (UTP)
 Shielded Twisted Pair (STP)
STP offers greater protection from interference and crosstalk due to shielding. But
it is heavier and costlier than UTP.
USE:
1. In local telephone communication
2. For digital data transmission over short distances up to 1 km
Advantages :





Easy to install and maintain
Simple
Inexpensive
Low weight
Suitable for small (Local) Networks
Disadvantages :
 Not suitable for long distance due to high attenuation.
 Low bandwidth support
 Low speed
Coaxial cable
 Coaxial cable consists of a solid copper wire core surrounded by a plastic
cladding shielded in a wire mesh.
 Shield prevents the noise by redirecting it to ground.
Types :
Coaxial cable comes in two sizes which are called thinnet and thicknet.
 Thicknet : segment length upto 500 m
 Thinnet : segment length upto 185 m
USE :
In TV channel communication
Advantages :
 Better than twisted wire cable.
 Popular for TV networks.
 Offers higher bandwidth & Speed
Disadvantages :
 Expensive than twisted wires.
 Not compatible with twisted wire cable.
Optical Fibres
 Thin strands of glass or glass like material designed to carry light from one
source to another.
 Source converts (Modulates) the data signal into light using LED (Light
Emitting Diodes) or LASER diodes and send it over the Optical fiber.
It consists of three parts :
1. The core : glass or plastic through which the light travels.
2. The cladding : covers the core and reflects light back to the core.
3. Protective coating : protects the fiber
Advantages :




Not affected by any kind of noise.
High transmission capacity
Speed of Light
Suitable for broadband communication
Disadvantages :




Installation requires care.
Connecting two Optical fibers is difficult.
Optical fibers are more difficult to solder
Most expensive