Computer - Overview

Today’s world is an information-rich world and it has become a necessity for everyone to know about computers. Purpose of this tutorial is to introduce you about computer and its fundamentals.

Functionalities of a computer

Any digital computer carries out five functions in gross terms:

Takes data as input.
Stores the data/instructions in its memory and use them when required.
Processes the data and converts it into useful information.
Generates the output
Controls all the above four steps.

Definition

Computer is an electronic data processing device which

accepts and stores data input,
processes the data input, and
generates the output in a required format.

Advantages

Following list demonstrates the advantages of computers in today's arena.

High Speed

Computer is a very fast device.
It is capable of performing calculation of very large amount of data.
The computer has units of speed in microsecond, nanosecond, and even the picosecond.
It can perform millions of calculations in a few seconds as compared to man who will spend many months for doing the same task.

Accuracy

In addition to being very fast, computers are very accurate.
The calculations are 100% error free.
Computers perform all jobs with 100% accuracy provided that correct input has been given.

Storage Capability

Memory is a very important characteristic of computers.
A computer has much more storage capacity than human beings.
It can store large amount of data.
It can store any type of data such as images, videos, text, audio and many others.

Diligence

Unlike human beings, a computer is free from monotony, tiredness and lack of concentration.
It can work continuously without any error and boredom.
It can do repeated work with same speed and accuracy.

Versatility

A computer is a very versatile machine.
A computer is very flexible in performing the jobs to be done.
This machine can be used to solve the problems related to various fields.
At one instance, it may be solving a complex scientific problem and the very next moment it may be playing a card game.

Reliability

A computer is a reliable machine.
Modern electronic components have long lives.
Computers are designed to make maintenance easy.

Automation

Computer is an automatic machine.
Automation means ability to perform the given task automatically.
Once a program is given to computer i.e., stored in computer memory, the program and instruction can control the program execution without human interaction.

Reduction in Paper Work

The use of computers for data processing in an organization leads to reduction in paper work and results in speeding up a process.
As data in electronic files can be retrieved as and when required, the problem of maintenance of large number of paper files gets reduced.

Reduction in Cost

Though the initial investment for installing a computer is high but it substantially reduces the cost of each of its transaction.

Disadvantages

Following list demonstrates the disadvantages of computers in today's arena

No I.Q

A computer is a machine that has no intelligence to perform any task.
Each instruction has to be given to computer.
A computer cannot take any decision on its own.

Dependency

It functions as per a user’s instruction, so it is fully dependent on human being

Environment

The operating environment of computer should be dust free and suitable.

No Feeling

Computers have no feelings or emotions.
It cannot make judgement based on feeling, taste, experience, and knowledge unlike a human being.

Computer - Applications

Following list demonstrates various applications of computers in today's arena.

Business

A computer has high speed of calculation, diligence, accuracy, reliability, or versatility which made it an integrated part in all business organisations.
Computer is used in business organisations for:

Payroll calculations
Budgeting
Sales analysis
Financial forecasting
Managing employees database
Maintenance of stocks etc.

Banking

Today banking is almost totally dependent on computer.
Banks provide following facilities:

Banks provide online accounting facility, which includes current balances, deposits, overdrafts, interest charges, shares, and trustee records.
ATM machines are making it even easier for customers to deal with banks.

Insurance

Insurance companies are keeping all records up-to-date with the help of computers. The insurance companies, finance houses and stock broking firms are widely using computers for their concerns.
Insurance companies are maintaining a database of all clients with information showing

procedure to continue with policies
starting date of the policies
next due installment of a policy
maturity date
interests due
survival benefits
bonus

Education

The computer has provided a lot of facilities in the education system.

The computer provides a tool in the education system known as CBE (Computer Based Education).
CBE involves control, delivery, and evaluation of learning.
The computer education is rapidly increasing the graph of number of computer students.
There are number of methods in which educational institutions can use computer to educate the students.
It is used to prepare a database about performance of a student and analysis is carried out on this basis.

Marketing

In marketing, uses of computer are following:

Advertising - With computers, advertising professionals create art and graphics, write and revise copy, and print and disseminate ads with the goal of selling more products.
At Home Shopping - Home shopping has been made possible through use of computerised catalogues that provide access to product information and permit direct entry of orders to be filled by the customers.

Health Care

Computers have become important part in hospitals, labs, and dispensaries. The computers are being used in hospitals to keep the record of patients and medicines. It is also used in scanning and diagnosing different diseases. ECG, EEG, Ultrasounds and CT Scans etc., are also done by computerised machines.
Some major fields of health care in which computers are used are:

Diagnostic System - Computers are used to collect data and identify cause of illness.
Lab-diagnostic System - All tests can be done and reports are prepared by computer.
Patient Monitoring System - These are used to check patient's signs for abnormality such as in Cardiac Arrest, ECG etc.
Pharma Information System - Computer checks Drug-Labels, Expiry dates, harmful drug’s side effects etc.
Surgery : Nowadays, computers are also used in performing surgery.

Engineering Design

Computers are widely used in Engineering purpose.
One of major areas is CAD (Computer aided design). That provides creation and modification of images. Some fields are:

Structural Engineering - Requires stress and strain analysis for design of Ships, Buildings, Budgets, Airplanes etc.
Industrial Engineering - Computers deal with design, implementation and improvement of integrated systems of people, materials and equipments.
Architectural Engineering - Computers help in planning towns, designing buildings, determining a range of buildings on a site using both 2D and 3D drawings.

Military

Computers are largely used in defence. Modern tanks, missiles, weapons etc. Military also employs computerised control systems. Some military areas where a computer has been used are:

Missile Control
Military Communication
Military Operation and Planning
Smart Weapons

Communication

Communication means to convey a message, an idea, a picture or speech that is received and understood clearly and correctly by the person for whom it is meant for. Some main areas in this category are:

E-mail
Chatting
Usenet
FTP
Telnet
Video-conferencing

Government

Computers play an important role in government. Some major fields in this category are:

Budgets
Sales tax department
Income tax department
Male/Female ratio
Computerization of voters lists
Computerization of driving licensing system
Computerization of PAN card
Weather forecasting

Computer - Generations

Generation in computer terminology is a change in technology a computer is/was being used. Initially, the generation term was used to distinguish between varying hardware technologies. But nowadays, generation includes both hardware and software, which together make up an entire computer system.
There are totally five computer generations known till date. Each generation has been discussed in detail along with their time period and characteristics. Here approximate dates against each generations have been mentioned which are normally accepted.
Following are the main five generations of computers

S.N.	Generation & Description
1	First Generation The period of first generation: 1946-1959. Vacuum tube based.
2	Second Generation The period of second generation: 1959-1965. Transistor based.
3	Third Generation The period of third generation: 1965-1971. Integrated Circuit based.
4	Fourth Generation The period of fourth generation: 1971-1980. VLSI microprocessor based.
5	Fifth Generation The period of fifth generation: 1980-onwards. ULSI microprocessor based

First Generation

The period of first generation was 1946-1959. The computers of first generation used vacuum tubes as the basic components for memory and circuitry for CPU (Central Processing Unit). These tubes, like electric bulbs, produced a lot of heat and were prone to frequent fusing of the installations, therefore, were very expensive and could be afforded only by very large organisations. In this generation mainly batch processing operating system were used. Punched cards, paper tape, and magnetic tape were used as input and output devices. The computers in this generation used machine code as programming language.

The main features of first generation are:

Vacuum tube technology
Unreliable
Supported machine language only
Very costly
Generated lot of heat
Slow input and output devices
Huge size
Need of A.C.
Non-portable
Consumed lot of electricity

Some computers of this generation were:

ENIAC
EDVAC
UNIVAC
IBM-701
IBM-650

Second Generation

The period of second generation was 1959-1965. In this generation transistors were used that were cheaper, consumed less power, more compact in size, more reliable and faster than the first generation machines made of vacuum tubes. In this generation, magnetic cores were used as primary memory and magnetic tape and magnetic disks as secondary storage devices. In this generation assembly language and high-level programming languages like FORTRAN, COBOL were used. The computers used batch processing and multiprogramming operating system.

The main features of second generation are:

Use of transistors
Reliable in comparison to first generation computers
Smaller size as compared to first generation computers
Generated less heat as compared to first generation computers
Consumed less electricity as compared to first generation computers
Faster than first generation computers
Still very costly
A.C. needed
Supported machine and assembly languages

Some computers of this generation were:

IBM 1620
IBM 7094
CDC 1604
CDC 3600
UNIVAC 1108

Third Generation

The period of third generation was 1965-1971. The computers of third generation used integrated circuits (IC's) in place of transistors. A single IC has many transistors, resistors and capacitors along with the associated circuitry. The IC was invented by Jack Kilby. This development made computers smaller in size, reliable and efficient. In this generation remote processing, time-sharing, multi-programming operating system were used. High-level languages (FORTRAN-II TO IV, COBOL, PASCAL PL/1, BASIC, ALGOL-68 etc.) were used during this generation.

The main features of third generation are:

IC used
More reliable in comparison to previous two generations
Smaller size
Generated less heat
Faster
Lesser maintenance
Still costly
A.C needed
Consumed lesser electricity
Supported high-level language

Some computers of this generation were:

IBM-360 series
Honeywell-6000 series
PDP(Personal Data Processor)
IBM-370/168
TDC-316

Fourth Generation

The period of fourth generation was 1971-1980. The computers of fourth generation used Very Large Scale Integrated (VLSI) circuits. VLSI circuits having about 5000 transistors and other circuit elements and their associated circuits on a single chip made it possible to have microcomputers of fourth generation. Fourth generation computers became more powerful, compact, reliable, and affordable. As a result, it gave rise to personal computer (PC) revolution. In this generation time sharing, real time, networks, distributed operating system were used. All the high-level languages like C, C++, DBASE etc., were used in this generation.

The main features of fourth generation are:

VLSI technology used
Very cheap
Portable and reliable
Use of PC's
Very small size
Pipeline processing
No A.C. needed
Concept of internet was introduced
Great developments in the fields of networks
Computers became easily available

Some computers of this generation were:

DEC 10
STAR 1000
PDP 11
CRAY-1(Super Computer)
CRAY-X-MP(Super Computer)

Fifth Generation

The period of fifth generation is 1980-till date. In the fifth generation, the VLSI technology became ULSI (Ultra Large Scale Integration) technology, resulting in the production of microprocessor chips having ten million electronic components. This generation is based on parallel processing hardware and AI (Artificial Intelligence) software. AI is an emerging branch in computer science, which interprets means and method of making computers think like human beings. All the high-level languages like C and C++, Java, .Net etc., are used in this generation.
AI includes:

Robotics
Neural Networks
Game Playing
Development of expert systems to make decisions in real life situations.
Natural language understanding and generation.

The main features of fifth generation are:

ULSI technology
Development of true artificial intelligence
Development of Natural language processing
Advancement in Parallel Processing
Advancement in Superconductor technology
More user friendly interfaces with multimedia features
Availability of very powerful and compact computers at cheaper rates

Some computer types of this generation are:

Desktop
Laptop
NoteBook
UltraBook
ChromeBook

Computer - Types

Computers can be broadly classified by their speed and computing power.

Sr.No.	Type	Specifications
1	PC (Personal Computer)	It is a single user computer system having moderately powerful microprocessor
2	WorkStation	It is also a single user computer system which is similar to personal computer but have more powerful microprocessor.
3	Mini Computer	It is a multi-user computer system which is capable of supporting hundreds of users simultaneously.
4	Main Frame	It is a multi-user computer system which is capable of supporting hundreds of users simultaneously. Software technology is different from minicomputer.
5	Supercomputer	It is an extremely fast computer which can execute hundreds of millions of instructions per second.

PC (Personal Computer)

A PC can be defined as a small, relatively inexpensive computer designed for an individual user. PCs are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. At home, the most popular use for personal computers is playing games and surfing Internet.
Although personal computers are designed as single-user systems, these systems are normally linked together to form a network. In terms of power, now-a-days High-end models of the Macintosh and PC offer the same computing power and graphics capability as low-end workstations by Sun Microsystems, Hewlett-Packard, and Dell.
Personal Computer

Workstation

Workstation is a computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other such types of applications which require a moderate amount of computing power and relatively high quality graphics capabilities.
Workstations generally come with a large, high-resolution graphics screen, large amount of RAM, inbuilt network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive.
Common operating systems for workstations are UNIX and Windows NT. Like PC, Workstations are also single-user computers like PC but are typically linked together to form a local-area network, although they can also be used as stand-alone systems.
Work Stations

Minicomputer

It is a midsize multi-processing system capable of supporting up to 250 users simultaneously.
Mini Computer

Mainframe

Mainframe is very large in size and is an expensive computer capable of supporting hundreds or even thousands of users simultaneously. Mainframe executes many programs concurrently and supports many simultaneous execution of programs
Main Frame

Supercomputer

Supercomputers are one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amount of mathematical calculations (number crunching). For example, weather forecasting, scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting).
Super Computer

Computer - Components

All types of computers follow a same basic logical structure and perform the following five basic operations for converting raw input data into information useful to their users.

Sr.No.	Operation	Description
1	Take Input	The process of entering data and instructions into the computer system
2	Store Data	Saving data and instructions so that they are available for processing as and when required.
3	Processing Data	Performing arithmetic, and logical operations on data in order to convert them into useful information.
4	Output Information	The process of producing useful information or results for the user, such as a printed report or visual display.
5	Control the workflow	Directs the manner and sequence in which all of the above operations are performed.

Input Unit

This unit contains devices with the help of which we enter data into computer. This unit makes link between user and computer. The input devices translate the information into the form understandable by computer.

CPU (Central Processing Unit)

CPU is considered as the brain of the computer. CPU performs all types of data processing operations. It stores data, intermediate results and instructions(program). It controls the operation of all parts of computer.
CPU itself has following three components

ALU(Arithmetic Logic Unit)
Memory Unit
Control Unit

Output Unit

Output unit consists of devices with the help of which we get the information from computer. This unit is a link between computer and users. Output devices translate the computer's output into the form understandable by users.

Computer - CPU

CPU consists of the following features:

CPU is considered as the brain of the computer.
CPU performs all types of data processing operations.
It stores data, intermediate results and instructions(program).
It controls the operation of all parts of computer.

CPU itself has following three components.

Memory or Storage Unit
Control Unit
ALU(Arithmetic Logic Unit)

Memory or Storage Unit

This unit can store instructions, data and intermediate results. This unit supplies information to the other units of the computer when needed. It is also known as internal storage unit or main memory or primary storage or Random access memory(RAM).
Its size affects speed, power and capability. Primary memory and secondary memory are two types of memories in the computer. Functions of memory unit are:

It stores all the data and the instructions required for processing.
It stores intermediate results of processing.
It stores final results of processing before these results are released to an output device.
All inputs and outputs are transmitted through main memory.

Control Unit

This unit controls the operations of all parts of computer but does not carry out any actual data processing operations.
Functions of this unit are:

It is responsible for controlling the transfer of data and instructions among other units of a computer.
It manages and coordinates all the units of the computer.
It obtains the instructions from the memory, interprets them, and directs the operation of the computer.
It communicates with Input/Output devices for transfer of data or results from storage.
It does not process or store data.

ALU(Arithmetic Logic Unit)

This unit consists of two subsections namely

Arithmetic section
Logic Section

Arithmetic Section

Function of arithmetic section is to perform arithmetic operations like addition, subtraction, multiplication and division. All complex operations are done by making repetitive use of above operations.

Logic Section

Function of logic section is to perform logic operations such as comparing, selecting, matching and merging of data.

Computer - Input Devices

Following are few of the important input devices which are used in a computer:

Keyboard
Mouse
Joy Stick
Light pen
Track Ball
Scanner
Graphic Tablet
Microphone
Magnetic Ink Card Reader(MICR)
Optical Character Reader(OCR)
Bar Code Reader
Optical Mark Reader(OMR)

Keyboard

Keyboard is the most common and very popular input device which helps in inputting data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.
Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.
The keys on the keyboard are as follows:

Sr.No	Keys	Description
1	Typing Keys	These keys include the letter keys (A-Z) and digit keys (0-9) which generally give same layout as that of typewriters.
2	Numeric Keypad	It is used to enter numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.
3	Function Keys	The twelve function keys are present on the keyboard which are arranged in a row at the top of the keyboard. Each function key has unique meaning and is used for some specific purpose.
4	Control keys	These keys provide cursor and screen control. It includes four directional arrow keys. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc).
5	Special Purpose Keys	Keyboard also contains some special purpose keys such as Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen.

Mouse

Mouse is most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base which senses the movement of mouse and sends corresponding signals to CPU when the mouse buttons are pressed.
Generally it has two buttons called left and right button and a wheel is present between the buttons. Mouse can be used to control the position of cursor on screen, but it cannot be used to enter text into the computer.

Advantages

Easy to use
Not very expensive
Moves the cursor faster than the arrow keys of keyboard.

Joystick

Joystick is also a pointing device which is used to move cursor position on a monitor screen. It is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in all four directions.
The function of joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing(CAD) and playing computer games.

Light Pen

Light pen is a pointing device which is similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube. When the tip of a light pen is moved over the monitor screen and pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.

Track Ball

Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on ball, pointer can be moved. Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button and a square.

Scanner

Scanner is an input device which works more like a photocopy machine. It is used when some information is available on a paper and it is to be transferred to the hard disc of the computer for further manipulation. Scanner captures images from the source which are then converted into the digital form that can be stored on the disc. These images can be edited before they are printed.
Scanner

Digitizer

Digitizer is an input device which converts analog information into digital form. Digitizer can convert a signal from the television or camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at. Digitizer is also known as Tablet or Graphics Tablet because it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for doing fine works of drawing and image manipulation applications.

Microphone

Microphone is an input device to input sound that is then stored in digital form. The microphone is used for various applications like adding sound to a multimedia presentation or for mixing music.

Magnetic Ink Card Reader(MICR)

MICR input device is generally used in banks because of a large number of cheques to be processed every day. The bank's code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable. This reading process is called Magnetic Ink Character Recognition (MICR). The main advantages of MICR is that it is fast and less error prone.
Magnetic Ink Card Reader(MICR)

Optical Character Reader(OCR)

OCR is an input device used to read a printed text. OCR scans text optically character by character, converts them into a machine readable code and stores the text on the system memory.
Optical Character Reader(OCR)

Bar Code Readers

Bar Code Reader is a device used for reading bar coded data (data in form of light and dark lines). Bar coded data is generally used in labelling goods, numbering the books etc. It may be a hand held scanner or may be embedded in a stationary scanner. Bar Code Reader scans a bar code image, converts it into an alphanumeric value which is then fed to the computer to which bar code reader is connected.
Barcode Reader

Optical Mark Reader(OMR)

OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked. It is specially used for checking the answer sheets of examinations having multiple choice questions.
Optical Mark Reader(OMR)

Computer - Output Devices

Following are few of the important output devices which are used in a computer.

Monitors
Graphic Plotter
Printer

Monitors

Monitors, commonly called as Visual Display Unit (VDU), are the main output device of a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular form. The sharpness of the image depends upon the number of pixels.
There are two kinds of viewing screen used for monitors.

Cathode-Ray Tube (CRT)
Flat- Panel Display

Cathode-Ray Tube (CRT) Monitor

The CRT display is made up of small picture elements called pixels. The smaller the pixels, the better the image clarity, or resolution. It takes more than one illuminated pixel to form whole character, such as the letter ‘e’ in the word help.
A finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes - fixed location on the screen where a standard character can be placed. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically. There are some disadvantages of CRT:

Large in Size
High power consumption

Flat-Panel Display Monitor

The flat-panel display refers to a class of video devices that have reduced volume, weight and power requirement in comparison to the CRT. You can hang them on walls or wear them on your wrists. Current uses of flat-panel displays include calculators, video games, monitors, laptop computer, graphics display.
The flat-panel display is divided into two categories:

Emissive Displays - The emissive displays are devices that convert electrical energy into light. Example are plasma panel and LED(Light-Emitting Diodes).
Non-Emissive Displays - The Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. Example is LCD(Liquid-Crystal Device)

Printers

Printer is an output device, which is used to print information on paper.
There are two types of printers:

Impact Printers
Non-Impact Printers

Impact Printers

The impact printers print the characters by striking them on the ribbon which is then pressed on the paper.
Characteristics of Impact Printers are the following:

Very low consumable costs
Very noisy
Useful for bulk printing due to low cost
There is physical contact with the paper to produce an image

These printers are of two types

Character printers
Line printers

Character Printers

Character printers are the printers which print one character at a time.
These are further divided into two types:

Dot Matrix Printer(DMP)
Daisy Wheel

Dot Matrix Printer

In the market one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come out to form a character that is why it is called Dot Matrix Printer.
Advantages

Inexpensive
Widely Used
Other language characters can be printed

Disadvantages

Slow Speed
Poor Quality

Daisy Wheel

Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower name) that is why it is called Daisy Wheel Printer. These printers are generally used for word-processing in offices which require a few letters to be sent here and there with very nice quality.
Advantages

More reliable than DMP
Better quality
The fonts of character can be easily changed

Disadvantages

Slower than DMP
Noisy
More expensive than DMP

Line Printers

Line printers are the printers which print one line at a time.

These are of further two types

Drum Printer
Chain Printer

Drum Printer

This printer is like a drum in shape so it is called drum printer. The surface of drum is divided into number of tracks. Total tracks are equal to size of paper i.e. for a paper width of 132 characters, drum will have 132 tracks. A character set is embossed on track. The different character sets available in the market are 48 character set, 64 and 96 characters set. One rotation of drum prints one line. Drum printers are fast in speed and can print 300 to 2000 lines per minute.
Advantages

Very high speed

Disadvantages

Very expensive
Characters fonts cannot be changed

Chain Printer

In this printer, chain of character sets are used so it is called Chain Printer. A standard character set may have 48, 64, or 96 characters.
Advantages

Character fonts can easily be changed.
Different languages can be used with the same printer.

Disadvantages

Noisy

Non-impact Printers

Non-impact printers print the characters without using ribbon. These printers print a complete page at a time so they are also called as Page Printers.
These printers are of two types

Laser Printers
Inkjet Printers

Characteristics of Non-impact Printers

Faster than impact printers.
They are not noisy.
High quality.
Support many fonts and different character size.

Laser Printers

These are non-impact page printers. They use laser lights to produce the dots needed to form the characters to be printed on a page.

Advantages

Very high speed
Very high quality output
Give good graphics quality
Support many fonts and different character size

Disadvantages

Expensive.
Cannot be used to produce multiple copies of a document in a single printing.

Inkjet Printers

Inkjet printers are non-impact character printers based on a relatively new technology. They print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality output with presentable features.
They make less noise because no hammering is done and these have many styles of printing modes available. Colour printing is also possible. Some models of Inkjet printers can produce multiple copies of printing also.

Advantages

High quality printing
More reliable

Disadvantages

Expensive as cost per page is high
Slow as compared to laser printer

Computer - Memory

A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored. The memory is divided into large number of small parts called cells. Each location or cell has a unique address which varies from zero to memory size minus one. For example if computer has 64k words, then this memory unit has 64 * 1024=65536 memory locations. The address of these locations varies from 0 to 65535.
Memory is primarily of three types

Cache Memory
Primary Memory/Main Memory
Secondary Memory

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory. It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them.

Advantages

The advantages of cache memory are as follows:

Cache memory is faster than main memory.
It consumes less access time as compared to main memory.
It stores the program that can be executed within a short period of time.
It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows:

Cache memory has limited capacity.
It is very expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed reside in main memory. It is divided into two subcategories RAM and ROM.

Characteristics of Main Memory

These are semiconductor memories
It is known as main memory.
Usually volatile memory.
Data is lost in case power is switched off.
It is working memory of the computer.
Faster than secondary memories.
A computer cannot run without primary memory.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing data/Information permanently. CPU directly does not access these memories instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory, and then CPU can access it. For example : disk, CD-ROM, DVD etc.

Characteristic of Secondary Memory

These are magnetic and optical memories
It is known as backup memory.
It is non-volatile memory.
Data is permanently stored even if power is switched off.
It is used for storage of data in a computer.
Computer may run without secondary memory.
Slower than primary memories.

Computer - Random Access Memory

RAM(Random Access Memory) is the internal memory of the CPU for storing data, program and program result. It is read/write memory which stores data until the machine is working. As soon as the machine is switched off, data is erased.
Access time in RAM is independent of the address that is, each storage location inside the memory is as easy to reach as other locations and takes the same amount of time. Data in the RAM can be accessed randomly but it is very expensive.
RAM is volatile, i.e. data stored in it is lost when we switch off the computer or if there is a power failure. Hence a backup uninterruptible power system(UPS) is often used with computers. RAM is small, both in terms of its physical size and in the amount of data it can hold.
RAM is of two types

Static RAM (SRAM)
Dynamic RAM (DRAM)

Static RAM (SRAM)

The word static indicates that the memory retains its contents as long as power is being supplied. However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6-transistors and no capacitors. Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis.
Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher. So SRAM is used as cache memory and has very fast access.

Characteristic of the Static RAM

It has long life
There is no need to refresh
Faster
Used as cache memory
Large size
Expensive
High power consumption

Dynamic RAM (DRAM)

DRAM, unlike SRAM, must be continually refreshed in order to maintain the data. This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second. DRAM is used for most system memory because it is cheap and small. All DRAMs are made up of memory cells which are composed of one capacitor and one transistor.

Characteristics of the Dynamic RAM

It has short data lifetime
Need to be refreshed continuously
Slower as compared to SRAM
Used as RAM
Lesser in size
Less expensive
Less power consumption

Computer - Read Only Memory

ROM stands for Read Only Memory. The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM, stores such instructions that are required to start a computer. This operation is referred to as bootstrap. ROM chips are not only used in the computer but also in other electronic items like washing machine and microwave oven.
ROM

Following are the various types of ROM

MROM (Masked ROM)

The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs which are inexpensive.

PROM (Programmable Read only Memory)

PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM program. Inside the PROM chip there are small fuses which are burnt open during programming. It can be programmed only once and is not erasable.

EPROM(Erasable and Programmable Read Only Memory)

The EPROM can be erased by exposing it to ultra-violet light for a duration of up to 40 minutes. Usually, an EPROM eraser achieves this function. During programming, an electrical charge is trapped in an insulated gate region. The charge is retained for more than ten years because the charge has no leakage path. For erasing this charge, ultra-violet light is passed through a quartz crystal window(lid). This exposure to ultra-violet light dissipates the charge. During normal use the quartz lid is sealed with a sticker.

EEPROM(Electrically Erasable and Programmable Read Only Memory)

The EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. Both erasing and programming take about 4 to 10 ms (milli second). In EEPROM, any location can be selectively erased and programmed. EEPROMs can be erased one byte at a time, rather than erasing the entire chip. Hence, the process of re-programming is flexible but slow.

Advantages of ROM

The advantages of ROM are as follows:

Non-volatile in nature
These cannot be accidentally changed
Cheaper than RAMs
Easy to test
More reliable than RAMs
These are static and do not require refreshing
Its contents are always known and can be verified

Computer - Motherboard

The motherboard serves as a single platform to connect all of the parts of a computer together. A motherboard connects CPU, memory, hard drives, optical drives, video card, sound card, and other ports and expansion cards directly or via cables. It can be considered as the backbone of a computer.
Mother Board

Features of Motherboard

A motherboard comes with following features:

Motherboard varies greatly in supporting various types of components.
Normally a motherboard supports a single type of CPU and few types of memories.
Video Cards, Hard disks, Sound Cards have to be compatible with motherboard to function properly
Motherboards, cases and power supplies must be compatible to work properly together.

Popular Manufacturers

Intel
ASUS
AOpen
ABIT
Biostar
Gigabyte
MSI

Description of Motherboard

The motherboard is mounted inside the case and is securely attached via small screws through pre-drilled holes. Motherboard contains ports to connect all of the internal components. It provides a single socket for CPU whereas for memory, normally one or more slots are available. Motherboards provide ports to attach floppy drive, hard drive, and optical drives via ribbon cables. Motherboard carries fans and a special port designed for power supply.
There is a peripheral card slot in front of the motherboard using which video cards, sound cards and other expansion cards can be connected to motherboard.
On the left side, motherboards carry a number of ports to connect monitor, printer, mouse, keyboard, speaker, and network cables. Motherboards also provide USB ports which allow compatible devices to be connected in plug-in/plug-out fashion for example, pen drive, digital cameras etc.

Computer - Memory Units

Memory unit is:

the amount of data that can be stored in the storage unit.
that in which storage capacity is expressed in terms of Bytes.

Following are the main memory storage units:

Sr.No.	Unit	Description
1	Bit (Binary Digit)	A binary digit is logical 0 and 1 representing a passive or an active state of a component in an electric circuit.
2	Nibble	A group of 4 bits is called nibble.
3	Byte	A group of 8 bits is called byte. A byte is the smallest unit which can represent a data item or a character.
4	Word	A computer word, like a byte, is a group of fixed number of bits processed as a unit which varies from computer to computer but is fixed for each computer. The length of a computer word is called word-size or word length and it may be as small as 8 bits or may be as long as 96 bits. A computer stores the information in the form of computer words.

Few higher storage units are following

Sr.No.	Unit	Description
1	Kilobyte (KB)	1 KB = 1024 Bytes
2	Megabyte (MB)	1 MB = 1024 KB
3	GigaByte (GB)	1 GB = 1024 MB
4	TeraByte (TB	1 TB = 1024 GB
5	PetaByte (PB)	1 PB = 1024 TB

Computer - Ports

What is a Port?

A port:

is a physical docking point using which an external device can be connected to the computer.
can also be programmatic docking point through which information flows from a program to computer or over the internet.

Characteristics

A port has the following characteristics:

External devices are connected to a computer using cables and ports.
Ports are slots on the motherboard into which a cable of external device is plugged in.
Examples of external devices attached via ports are mouse, keyboard, monitor, microphone, speakers etc.

Following are few important types of ports:

Serial Port

Used for external modems and older computer mouse
Two versions : 9 pin, 25 pin model
Data travels at 115 kilobits per second

Parallel Port

Used for scanners and printers
Also called printer port
25 pin model
Also known as IEEE 1284-compliant Centronics port

PS/2 Port

Used for old computer keyboard and mouse
Also called mouse port
Most of the old computers provide two PS/2 port, each for mouse and keyboard
Also known as IEEE 1284-compliant Centronics port

Universal Serial Bus (or USB) Port

It can connect all kinds of external USB devices such as external hard disk, printer, scanner, mouse, keyboard etc.
It was introduced in 1997.
Most of the computers provide two USB ports as minimum.
Data travels at 12 megabits per seconds
USB compliant devices can get power from a USB port

VGA Port

Connects monitor to a computer's video card.
Has 15 holes.
Similar to serial port connector but serial port connector has pins, it has holes.

Power Connector

Three-pronged plug
Connects to the computer's power cable that plugs into a power bar or wall socket

Firewire Port

Transfers large amount of data at very fast speed.
Connects camcorders and video equipments to the computer
Data travels at 400 to 800 megabits per seconds
Invented by Apple
Three variants : 4-Pin FireWire 400 connector, 6-Pin FireWire 400 connector and 9-Pin FireWire 800 connector

Modem Port

Connects a PC's modem to the telephone network

Ethernet Port

Connects to a network and high speed Internet.
Connect network cable to a computer.
This port resides on an Ethernet Card.
Data travels at 10 megabits to 1000 megabits per seconds depending upon the network bandwidth.

Game Port

Connect a joystick to a PC
Now replaced by USB.

Digital Video Interface, DVI port

Connects Flat panel LCD monitor to the computer's high end video graphic cards.
Very popular among video card manufacturers.

Sockets

Connect microphone, speakers to sound card of the computer

Computer - Hardware

Hardware represents the physical and tangible components of a computer i.e. the components that can be seen and touched.
Examples of Hardware are following:

Input devices -- keyboard, mouse etc.
Output devices -- printer, monitor etc.
Secondary storage devices -- Hard disk, CD, DVD etc.
Internal components -- CPU, motherboard, RAM etc.

Relationship between Hardware and Software

Hardware and software are mutually dependent on each other. Both of them must work together to make a computer produce a useful output.
Software cannot be utilized without supporting hardware.
Hardware without set of programs to operate upon cannot be utilized and is useless.
To get a particular job done on the computer, relevant software should be loaded into the hardware
Hardware is a one-time expense.
Software development is very expensive and is a continuing expense.
Different software applications can be loaded on a hardware to run different jobs.
A software acts as an interface between the user and the hardware.
If hardware is the 'heart' of a computer system, then software is its 'soul'. Both are complimentary to each other.

Computer - Software

Software is a set of programs, which is designed to perform a well-defined function. A program is a sequence of instructions written to solve a particular problem.
There are two types of software

System Software
Application Software

System Software

The system software is collection of programs designed to operate, control, and extend the processing capabilities of the computer itself. System software are generally prepared by computer manufactures. These software products comprise of programs written in low-level languages which interact with the hardware at a very basic level. System software serves as the interface between hardware and the end users.
Some examples of system software are Operating System, Compilers, Interpreter, Assemblers etc.

Features of system software are as follows:

Close to system
Fast in speed
Difficult to design
Difficult to understand
Less interactive
Smaller in size
Difficult to manipulate
Generally written in low-level language

Application Software

Application software products are designed to satisfy a particular need of a particular environment. All software applications prepared in the computer lab can come under the category of Application software.
Application software may consist of a single program, such as a Microsoft's notepad for writing and editing simple text. It may also consist of a collection of programs, often called a software package, which work together to accomplish a task, such as a spreadsheet package.
Examples of Application software are following:

Payroll Software
Student Record Software
Inventory Management Software
Income Tax Software
Railways Reservation Software
Microsoft Office Suite Software
Microsoft Word
Microsoft Excel
Microsoft Powerpoint

Features of application software are as follows:

Close to user
Easy to design
More interactive
Slow in speed
Generally written in high-level language
Easy to understand
Easy to manipulate and use
Bigger in size and requires large storage space

Computer - Number System

When we type some letters or words, the computer translates them in numbers as computers can understand only numbers. A computer can understand positional number system where there are only a few symbols called digits and these symbols represent different values depending on the position they occupy in the number.
A value of each digit in a number can be determined using

The digit
The position of the digit in the number
The base of the number system (where base is defined as the total number of digits available in the number system).

Decimal Number System

The number system that we use in our day-to-day life is the decimal number system. Decimal number system has base 10 as it uses 10 digits from 0 to 9. In decimal number system, the successive positions to the left of the decimal point represent units, tens, hundreds, thousands and so on.
Each position represents a specific power of the base (10). For example, the decimal number 1234 consists of the digit 4 in the units position, 3 in the tens position, 2 in the hundreds position, and 1 in the thousands position, and its value can be written as

(1x1000)+ (2x100)+ (3x10)+ (4xl)
(1x10³)+ (2x10²)+ (3x10¹)+ (4xl0⁰)
1000 + 200 + 30 + 4
1234

As a computer programmer or an IT professional, you should understand the following number systems which are frequently used in computers.

S.N.	Number System and Description
1	Binary Number System Base 2. Digits used : 0, 1
2	Octal Number System Base 8. Digits used : 0 to 7
3	Hexa Decimal Number System Base 16. Digits used : 0 to 9, Letters used : A- F

Binary Number System

Characteristics of binary number system are as follows:

Uses two digits, 0 and 1.
Also called base 2 number system
Each position in a binary number represents a 0 power of the base (2). Example 2⁰
Last position in a binary number represents a x power of the base (2). Example 2^x where x represents the last position - 1.

Example

Binary Number : 10101₂
Calculating Decimal Equivalent:

Step	Binary Number	Decimal Number
Step 1	10101₂	((1 x 2⁴) + (0 x 2³) + (1 x 2²) + (0 x 2¹) + (1 x 2⁰))₁₀
Step 2	10101₂	(16 + 0 + 4 + 0 + 1)₁₀
Step 3	10101₂	21₁₀

Note : 10101₂ is normally written as 10101.

Octal Number System

Characteristics of octal number system are as follows:

Uses eight digits, 0,1,2,3,4,5,6,7.
Also called base 8 number system
Each position in an octal number represents a 0 power of the base (8). Example 8⁰
Last position in an octal number represents a x power of the base (8). Example 8^x where x represents the last position - 1.

Example

Octal Number : 12570₈
Calculating Decimal Equivalent:

Step	Octal Number	Decimal Number
Step 1	12570₈	((1 x 8⁴) + (2 x 8³) + (5 x 8²) + (7 x 8¹) + (0 x 8⁰))₁₀
Step 2	12570₈	(4096 + 1024 + 320 + 56 + 0)₁₀
Step 3	12570₈	5496₁₀

Note : 12570₈ is normally written as 12570.

Hexadecimal Number System

Characteristics of hexadecimal number system are as follows:

Uses 10 digits and 6 letters, 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F.
Letters represents numbers starting from 10. A = 10. B = 11, C = 12, D = 13, E = 14, F = 15.
Also called base 16 number system
Each position in a hexadecimal number represents a 0 power of the base (16). Example 16⁰
Last position in a hexadecimal number represents a x power of the base (16). Example 16^x where x represents the last position - 1.

Example

Hexadecimal Number : 19FDE₁₆
Calculating Decimal Equivalent:

Step	Binary Number	Decimal Number
Step 1	19FDE₁₆	((1 x 16⁴) + (9 x 16³) + (F x 16²) + (D x 16¹) + (E x 16⁰))₁₀
Step 2	19FDE₁₆	((1 x 16⁴) + (9 x 16³) + (15 x 16²) + (13 x 16¹) + (14 x 16⁰))₁₀
Step 3	19FDE₁₆	(65536+ 36864 + 3840 + 208 + 14)₁₀
Step 4	19FDE₁₆	106462₁₀

Note : 19FDE₁₆ is normally written as 19FDE.

Computer - Number Conversion

There are many methods or techniques which can be used to convert numbers from one base to another. We'll demonstrate here the following:

Decimal to Other Base System
Other Base System to Decimal
Other Base System to Non-Decimal
Shortcut method - Binary to Octal
Shortcut method - Octal to Binary
Shortcut method - Binary to Hexadecimal
Shortcut method - Hexadecimal to Binary

Decimal to Other Base System

steps

Step 1 - Divide the decimal number to be converted by the value of the new base.
Step 2 - Get the remainder from Step 1 as the rightmost digit (least significant digit) of new base number.
Step 3 - Divide the quotient of the previous divide by the new base.
Step 4 - Record the remainder from Step 3 as the next digit (to the left) of the new base number.

Repeat Steps 3 and 4, getting remainders from right to left, until the quotient becomes zero in Step 3.
The last remainder thus obtained will be the most significant digit (MSD) of the new base number.

Example

Decimal Number : 29₁₀
Calculating Binary Equivalent:

Step	Operation	Result	Remainder
Step 1	29 / 2	14	1
Step 2	14 / 2	7	0
Step 3	7 / 2	3	1
Step 4	3 / 2	1	1
Step 5	1 / 2	0	1

As mentioned in Steps 2 and 4, the remainders have to be arranged in the reverse order so that the first remainder becomes the least significant digit (LSD) and the last remainder becomes the most significant digit (MSD).
Decimal Number : 29₁₀ = Binary Number : 11101_2.

Other base system to Decimal System

Steps

Step 1 - Determine the column (positional) value of each digit (this depends on the position of the digit and the base of the number system).
Step 2 - Multiply the obtained column values (in Step 1) by the digits in the corresponding columns.
Step 3 - Sum the products calculated in Step 2. The total is the equivalent value in decimal.

Example

Binary Number : 11101₂
Calculating Decimal Equivalent:

Step	Binary Number	Decimal Number
Step 1	11101₂	((1 x 2⁴) + (1 x 2³) + (1 x 2²) + (0 x 2¹) + (1 x 2⁰))₁₀
Step 2	11101₂	(16 + 8 + 4 + 0 + 1)₁₀
Step 3	11101₂	29₁₀

Binary Number : 11101₂ = Decimal Number : 29₁₀

Other Base System to Non-Decimal System

Steps

Step 1 - Convert the original number to a decimal number (base 10).
Step 2 - Convert the decimal number so obtained to the new base number.

Example

Octal Number : 25₈
Calculating Binary Equivalent:

Step 1 : Convert to Decimal

Step	Octal Number	Decimal Number
Step 1	25₈	((2 x 8¹) + (5 x 8⁰))₁₀
Step 2	25₈	(16 + 5 )₁₀
Step 3	25₈	21₁₀

Octal Number : 25₈ = Decimal Number : 21₁₀

Step 2 : Convert Decimal to Binary

Step	Operation	Result	Remainder
Step 1	21 / 2	10	1
Step 2	10 / 2	5	0
Step 3	5 / 2	2	1
Step 4	2 / 2	1	0
Step 5	1 / 2	0	1

Decimal Number : 21₁₀ = Binary Number : 10101₂
Octal Number : 25₈ = Binary Number : 10101₂

Shortcut method - Binary to Octal

Steps

Step 1 - Divide the binary digits into groups of three (starting from the right).
Step 2 - Convert each group of three binary digits to one octal digit.

Example

Binary Number : 10101₂
Calculating Octal Equivalent:

Step	Binary Number	Octal Number
Step 1	10101₂	010 101
Step 2	10101₂	2₈ 5₈
Step 3	10101₂	25₈

Binary Number : 10101₂ = Octal Number : 25₈

Shortcut method - Octal to Binary

Steps

Step 1 - Convert each octal digit to a 3 digit binary number (the octal digits may be treated as decimal for this conversion).
Step 2 - Combine all the resulting binary groups (of 3 digits each) into a single binary number.

Example

Octal Number : 25₈
Calculating Binary Equivalent:

Step	Octal Number	Binary Number
Step 1	25₈	2₁₀ 5₁₀
Step 2	25₈	010₂ 101₂
Step 3	25₈	010101₂

Octal Number : 25₈ = Binary Number : 10101₂

Shortcut method - Binary to Hexadecimal

Steps

Step 1 - Divide the binary digits into groups of four (starting from the right).
Step 2 - Convert each group of four binary digits to one hexadecimal symbol.

Example

Binary Number : 10101₂
Calculating hexadecimal Equivalent:

Step	Binary Number	Hexadecimal Number
Step 1	10101₂	0001 0101
Step 2	10101₂	1₁₀ 5₁₀
Step 3	10101₂	15₁₆

Binary Number : 10101₂ = Hexadecimal Number : 15₁₆

Shortcut method - Hexadecimal to Binary

steps

Step 1 - Convert each hexadecimal digit to a 4 digit binary number (the hexadecimal digits may be treated as decimal for this conversion).
Step 2 - Combine all the resulting binary groups (of 4 digits each) into a single binary number.

Example

Hexadecimal Number : 15₁₆
Calculating Binary Equivalent:

Step	Hexadecimal Number	Binary Number
Step 1	15₁₆	1₁₀ 5₁₀
Step 2	15₁₆	0001₂ 0101₂
Step 3	15₁₆	00010101₂

Hexadecimal Number : 15₁₆ = Binary Number : 10101₂

Computer - Data and Information

What is data?

Data can be defined as a representation of facts, concepts or instructions in a formalized manner which should be suitable for communication, interpretation, or processing by human or electronic machine.
Data is represented with the help of characters like alphabets (A-Z,a-z), digits (0-9) or special characters(+,-,/,*,<,>,= etc.).
Raw Computer Data

What is Information?

Information is organised or classified data which has some meaningful values for the receiver.
Information is the processed data on which decisions and actions are based.
For the decision to be meaningful, the processed data must qualify for the following characteristics:

Timely - Information should be available when required.
Accuracy - Information should be accurate.
Completeness - Information should be complete.

Data Processing Cycle

Data processing is the re-structuring or re-ordering of data by people or machine to increase their usefulness and add values for particular purpose. Data processing consists of basic steps input, processing and output. These three steps constitute the data processing cycle.
Computer Data

Input - In this step the input data is prepared in some convenient form for processing. The form will depend on the processing machine. For example, when electronic computers are used, the input data could be recorded on any one of several types of input medium, such as magnetic disks, tapes and so on.
Processing - In this step input data is changed to produce data in a more useful form. For example, pay-checks may be calculated from the time cards, or a summary of sales for the month may be calculated from the sales orders.
Output - Here the result of the proceeding processing step are collected. The particular form of the output data depends on the use of the data. For example, output data may be pay-checks for employees.

Computer - Networking

What is a Computer Network?

A computer network is a system in which multiple computers are connected to each other to share information and resources.
Computer Networks

Characteristics of a computer network

Share Resources from one computer to another
Create files and store them in one computer, access those files from the other computer(s) connected over the network
Connect a printer, scanner, or a fax machine to one computer within the network and let other computers of the network use the machines available over network.

Following is the list of hardware's required to setup a computer network.

Network Cables
Distributors
Routers
Internal Network Cards
External Network Cards

Network Cables

Network cables are used to connect computers. The most commonly used cable is Category 5 cable RJ-45.

Distributors

A computer can be connected to another one via a serial port but if we need to connect many computers to produce a network, this serial connection will not work. The solution is to use a central body to which other computers, printers, scanners etc. can be connected and then this body will manage or distribute network traffic.
Network Distributors

Router

A router is a type of device which acts as the central point among computers and other devices that are part of a network. A router is equipped with holes called ports and computers and other devices are connected to a router using network cables. Now-a-days router comes in wireless modes using which computers can be connected without any physical cable.
Network Router

Network Card

Network card is a necessary component of a computer without which a computer cannot be connected over a network. It is also known as network adapter or Network Interface Card (NIC). Most branded computers have network card pre-installed. Network cards are of two types : Internal and External Network Cards.

Internal Network Cards

Motherboard has a slot for internal network card where it is to be inserted. Internal network cards are of two types in which first type uses Peripheral Component Interconnect (PCI) connection while the second type uses Industry Standard Architecture (ISA). Network cables are required to provide network access.

External Network Cards

External network cards come in two flavours : Wireless and USB based. Wireless network card need to be inserted into the motherboard but no network cable is required to connect to network

Universal Serial Bus (USB)
USB card are easy to use and connect via USB port. Computers automatically detect USB card and can install the drivers required to support the USB network card automatically.
Data Card

Computer - Operating System

It is a program with following features:

An operating system is a program that acts as an interface between the software and the computer hardware.
It is an integrated set of specialised programs that are used to manage overall resources and operations of the computer.
It is specialised software that controls and monitors the execution of all other programs that reside in the computer, including application programs and other system software.

Objectives of Operating System

To make a computer system convenient to use in an efficient manner
To hide the details of the hardware resources from the users
To provide users a convenient interface to use the computer system
To act as an intermediary between the hardware and its users and making it easier for the users to access and use other resources
To manage the resources of a computer system
To keep track of who is using which resource, granting resource requests, according for resource using and mediating conflicting requests from different programs and users
To provide efficient and fair sharing of resources among users and programs

Characteristics of Operating System

Memory Management -- keeps tracks of primary memory i.e. what part of it is in use by whom, what part is not in use etc. and allocates the memory when a process or program requests it.
Processor Management -- allocates the processor(CPU) to a process and deallocates processor when it is no longer required.
Device Management -- keeps track of all devices. This is also called I/O controller that decides which process gets the device, when, and for how much time.
File Management -- allocates and de-allocates the resources and decides who gets the resources.
Security -- prevents unauthorized access to programs and data by means of passwords and similar other techniques.
Job accounting -- keeps track of time and resources used by various jobs and/or users.
Control over system performance -- records delays between request for a service and from the system.
Interaction with the operators -- The interaction may take place via the console of the computer in the form of instructions. Operating System acknowledges the same, does the corresponding action and informs the operation by a display screen.
Error-detecting aids -- Production of dumps, traces, error messages and other debugging and error-detecting methods.
Coordination between other software and users -- Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems.

Computer - Internet and Intranet

Internet

It is a worldwide system which has the following characteristics:

Internet is a world-wide / global system of interconnected computer networks.
Internet uses the standard Internet Protocol (TCP/IP)
Every computer in internet is identified by a unique IP address.
IP Address is a unique set of numbers (such as 110.22.33.114) which identifies a computer’s location.
A special computer DNS (Domain Name Server) is used to give name to the IP Address so that user can locate a computer by a name.
For example, a DNS server will resolve a name http://www.tutorialspoint.com to a particular IP address to uniquely identify the computer on which this website is hosted.
Internet is accessible to every user all over the world.

Intranet

Intranet is system in which multiple PCs are connected to each other.
PCs in intranet are not available to the world outside the intranet.
Usually each company or organization has their own Intranet network and members/employees of that company can access the computers in their intranet.
Each computer in Intranet is also identified by an IP Address which is unique among the computers in that Intranet.

Similarities in Internet and Intranet

Intranet uses the internet protocols such as TCP/IP and FTP.
Intranet sites are accessible via web browser in similar way as websites in internet. But only members of Intranet network can access intranet hosted sites.
In Intranet, own instant messengers can be used as similar to yahoo messenger/ gtalk over the internet.

Differences in Internet and Intranet

Internet is general to PCs all over the world whereas Intranet is specific to few PCs.
Internet has wider access and provides a better access to websites to large population whereas Intranet is restricted.
Internet is not as safe as Intranet as Intranet can be safely privatized as per the need.

Computer - How to Buy?

This chapter gives the following information:

In this guide, we'll help you to buy a desktop on component by component basis.
As desktops are highly customizable, so it is better to learn about main parts and then go to manufacturer or retailer shop or site instead of looking at some specific model directly.
Popular desktop brands are Dell, Lenovo, HP and Apple.
Compare the desktops based on their specifications and base price.

Monitor

Size - It is the diagonal size of the LCD screen. Larger the area, bigger the picture screen. A bigger picture is preferable for movie watching and gaming. It will increase productivity as well.
Resolution - This is the number of pixels on the screen. For example, 24-inch display is 1920x1200 (width by length) and 22-inch display which is 1680x1050. High resolution provides better picture quality and a nice gaming experience.
Inputs - Now-a-days monitors can accept inputs from cable as well apart from computer. They also can have USB ports.
Stand - Some monitors come with adjustable stands while some may not.
Recommended - 24 Inch LCD.

Operating System

Operating System is the main software of the computer as everything will run on it in one form or other.
There are primarily three choices : Windows, Linux, Apple OS X.
Linux is free but people generally do not use it for home purpose.
Apple OS X works only on Apple Desktops.
Windows 7 is very popular among desktop users.
Most of the computers come pre-equipped with Windows 7 Starter edition.
Windows 8 is recently introduced and is available in market.
Windows 7 and Windows 8 come in multiple versions from starter, home basic, home premium, professional, ultimate and enterprise editions.
As edition version increases, their features list and price increases.
Recommended - Windows 7 Home Premium.

Optical Drive (CD / DVD / Blu-ray)

Optical drive is the drive on a computer which is responsible for using CD, DVD and Blu-ray discs.
Now-a-days, DVD burners are industry standards.
DVD Burner can burn CD, DVD and play them.
DVD Burner is cheaper than Blu-ray drives.
Blu-ray drives can play HD movies but are costlier component.
Recommended - DVD Burner.

Memory

RAM is considered as Computer Memory as performance of a computer is directly proportional to its memory and processor.
Today's software and operating system require high memory.
Today commonly used RAM is DDR3 which operates at 1066Mhz
As per Windows 7, 1 GB is the minimum RAM required to function properly.
Recommended - 4 GB.

Hard Drive

Hard disk is used for storage purpose. Higher the capacity, more data you can save in it.
Now-a-days computers are equipped with 500GB hard drive which can be extended to 2TB.
Most hard drives in desktop operate at the standard performance speed of 7200RPM.
Recommended - 500GB.

CPU

Frequency (GHz) - This determines speed of the processor. More the speed, better the CPU.
Cores - Now-a-days CPUs come with more than one core, which is like having more than one CPU in the computer. Programs which can take advantage of multi-core environment will run faster on such machines.
Brand - Intel or AMD. Both are equivalent. Intel is in lead.
Cache - Higher the L1, L2 cache, better the CPU performance
Recommended - Intel Core i3 i3-3225 3.30 GHz Processor.

Computer - Available Courses

Now–a-days, various types of educational courses are provided by educational institutions.
Computer Training

Course	Name	Duration (years)	Minimum Qualification
B.C.A	Bachelor of Computer Applications	3	10+2
P.G.D.C.A	Post Graduate Diploma in Computer Applications	1	Graduation
M.C.A	Master of Computer Applications	3	Graduation
B.Sc.(CS)	Bachelor of Science (Computer Science)	3	10+2
M.Sc.(CS)	Master of Science (Computer Science)	2	Graduation
B.Tech.(CSE)	Bachelor of Technology (Computer Science and Engineering)	4	10+2
B.Tech.(IT)	Bachelor of Technology (Information Technology)	4	10+2
M.Tech.(CSE)	Master of Technology (Computer Science and Engineering)	2	B.Tech / B.E.
M.Tech.(IT)	Master of Technology (Information Technology)	2	B.Tech / B.E
B.E.(CSE)	Bachelor of Engineering (Computer Science and Engineering)	4	10+2
B.E.(IT)	Bachelor of Engineering (Information Technology)	4	10+2

Diploma Courses

Apart from regular degree courses, now computer centers also provide short term courses (from 3 months to 1 year).
Online courses are also getting popularity.

Computer Basics
Programming Language Trainings
Hardware Trainings
Network Certifications

The following resources contain additional information on Computer Basics. Please use them to get more in-depth knowledge on this topic.

Useful Links on Computer Basics

Computer Basics by BBC − An introduction to computers including computer parts and health and safety.
Some Basic Terminology − Various computer terms has been explained in simple language.
Basic Computer Literacy Information − A quick go through Basic Computer Literacy Information.