Technology Homesite

oblems, the RAM is very easy to replace in the HP Pavilion dv6000.

 

Business

A has high speed of calculation, diligence, accuracy, reliability, or versatility which made it an integrated part in all business organisations.
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 .
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 has provided a lot of facilities in the education system.

• The provides a tool in the education system known as CBE ( Based Education).
• CBE involves control, delivery, and evaluation of learning.
• The education is rapidly increasing the graph of number of students.
• There are number of methods in which educational institutions can use 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 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 and identify cause of illness.
• Lab-diagnostic System - All tests can be done and reports are prepared by .
• Patient Monitoring System - These are used to check patient's signs for abnormality such as in Cardiac Arrest, ECG etc.
• Pharma Information System - 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 ( 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 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

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

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

PC (Personal )

A PC can be defined as a small, relatively inexpensive designed for an individual user. PCs are based on the microprocessor technology that enables manufacturers to put an entire on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management . At home, the most popular use for personal computers is playing games and surfing .
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.

Workstation

Workstation is a used for engineering (CAD/CAM), desktop publishing, development, and other such of 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 , 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.

Minicomputer

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

Mainframe

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

Supercomputer

Supercomputers are one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized 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 (e.g. in petrochemical prospecting).

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

Sr.No.	Operation	Description
1	Take Input	The process of entering and instructions into the system
2	Store	Saving and instructions so that they are available for processing as and when required.
3	Processing	Performing arithmetic, and logical operations on 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 into . This unit makes link between user and . The translate the information into the form understandable by .

(Central Processing Unit)

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

• ALU(Arithmetic Logic Unit)
• Unit
• Control Unit

Output Unit

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

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.

Following are few of the important which are used in a :

• 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 to the . 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 .
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 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 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 .

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 Aided Designing(CAD) and playing 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 .

Track Ball

Track ball is an input device that is mostly used in notebook or laptop , 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 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.

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 . They can be used by the 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 into binary inputs. A graphic tablet as digitizer is used for doing fine works of drawing and image manipulation .

Microphone

Microphone is an input device to input sound that is then stored in digital form. The microphone is used for various 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.

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 .

Bar Code Readers

Bar Code Reader is a device used for reading bar coded ( in form of light and dark lines). Bar coded 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 to which bar code reader is connected.

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.

 

Following are few of the important which are used in a .

• Monitors
• Graphic Plotter
• Printer

Monitors

Monitors, commonly called as Visual Display Unit (VDU), are the main output device of a . 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 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 , 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 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

• Character printers
• Line printers

Character Printers

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

• 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

• 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

• 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

 

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.

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

• Static (SRAM)
• Dynamic (DRAM)

Static (SRAM)

The word static indicates that the retains its contents as long as power is being supplied. However, 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 and has very fast access.

Characteristic of the Static

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

Dynamic (DRAM)

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

Characteristics of the Dynamic

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

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


following are the various of

MROM (Masked )

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

PROM (Programmable Read only )

PROM is read-only 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 )

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 )

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

The advantages of 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

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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.


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.

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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

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What is a Port?

A port:

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

Characteristics

A port has the following characteristics:

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

Following are few important of :

Serial Port

• Used for external modems and older mouse
• Two versions : 9 pin, 25 pin model
• 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 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 as minimum.
• travels at 12 megabits per seconds
• USB compliant devices can get power from a USB port

VGA Port

• Connects monitor to a '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 's power cable that plugs into a power bar or wall socket

Firewire Port

• Transfers large amount of at very fast speed.
• Connects camcorders and video equipments to the
• 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 .
• Connect network cable to a .
• This port resides on an Ethernet Card.
• 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 's high end video graphic cards.
• Very popular among video card manufacturers.

Sockets

• Connect microphone, speakers to sound card of the

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