Generations of computersFirst 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 softwareb) 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 translatorA 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.AssemblerIt is used to convert the assembly language into machine language consists of mnemonic codes which are difficult to learn and is machine dependent.CompilerIt 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 devicesA 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 devicesKeyboard, mouse, light pen, scanner, microphone, trackball, joy stick, barcode reader, web camera.KeyboardKeyboard 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 in 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

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 PrinterEpson 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 It can be erased by using strong UV light, then rewritten.

(c)EEPROM It can be programmed several times, but can be erased by using electrical signals.

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 = Binary Digit 8 bits = 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 The information / data carry from one end to another in the network by channel.

Baud & bits per second (bps) 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) =

1024 Bytes. 1 kbps (kilobits Per Second) = 1024

bits.

1 Mbps (Mega bits per second)= 1024 Kbps

Bandwidth 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 optico single-modeo 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