computer system – Computer system parts – Secondary Storage – USB Flash Drive

computer system

Computer is a group of electronic device used to process data. Or it can also be said that a computer is an electronic device that can perform a variety of operation in accordance with a set of instructions called program. A computer is an automatic programmable electronic device which accepts data, stores it internally and generates the desired results.

Fact file – computer is an electronic device that can perform a variety of operations according to a set of instructions called program.

This final result is accurate according to given commands and instruction.

A computer is used essentially as a data process The terms data and information are very commonly used.
essentially as a data processor. You must clearly understand the difference between the two.

Data : Data in computer terminology mean raw fa
computer terminology mean raw facts and figures. For example ‘Tom’, “1900”, ‘A’. “1234” are data. Data is processe to form information. After processing what we get is meaningful data. This data is known as information.

do you know – computer can access and process data millions of times faster than human beings computer can do a lot of different tasks such as playing games railway reservation weather forecasting error detection and confrolling the flight of a space aircraft etc.


Data is aggregated and summarized in various meaningful ways to form information. For example Tom whose roll no. is 1234 has you grade A is an information as it is conveying some meaning.

Functioning of a Computer

Before we start discuss the functioning of a computer, let us understand the way we function. To understand this, we will take some examples.

(i) Consider a case when your mother asks you to bring a cake and pastries from the market. You go to the market purchase both the thing and gave it to your mother.

(ii) You want to talk to one of your friends. This phone number is 2671040. So you dial up the number and speak to your friend.

(iii) If you want to make mango shake by blender, you put mango milk, sugar in flask and switch on the blender. After grinding, we get mango shake.

Above examples illustrate the way we human beings function. Consider all the three examples. There are certain things common in them. In all the examples certain things were needed to work upon, the actual work was then carried out accordingly and finally the result was obtained.

All the examples undergo these three stages. The first stage (things to work upon) called input stage. The second stage (the actual work being performed) is called proces stage and the third stage (the result) is called output stage. Certain input is needed to accomplish a task, a process is carried out on the input to obtain the desired output.



things to work upon 


the actual work taking  place 


the result

example 1; mummy order of purchasing cake and pastriesgoing to bazaar and purchasing .purchased cake and pastries 
example 2: your desire to make a phone call at number 2751045make a phone callchat with your friend 

Functional Components of a Computer System

Since a computer follows input process output cycle, the first stage is performed in computer by input unit, second stage is performed by its central processing unit and the third stage is performed by output unit. And all this is done with the help of memory. Memory is the brain of computer which holds the data during processing. Thus the basic structure of a computer is as shown below.

know the fact  – a computer takes an input carries out a process upon it and produces  outpu

functional components of a computer system
functional components of a computer system

The main memory holds the input and intermediate output during the processing.

fact file   – memory is the storage brain of computer , which holds the data during processing 

(1) The Input Unit

As you know that the input unit is responsible for accepting input i.e. data and instructions from the user. This work is accomplished with the help of input devices. Device, in general; refers to an equipment. Over the years, many input devices have been built in many forms for many special purposes.
For instance, keyboard is used for a different purpose and a mouse or a trackball is used for a different purpose. Let us learn about some most common input devices

tips – the input unit of a computer system is responsible for input – phase, cpu ( central processing unit ) is responsible for process phase , and output unit is responsible for output  phase 



You all are familiar with keyboard. It is an input device used to type letters, digits and commands. It has keys for alphabets, digits, symbols like +, -;:;*, $. # etc. and some special keys that can be used for moving cursor or deleting a letter or confirming a command etc. when a key is pressed a signal is sent to the computer which is decoded there to determine which key has been pre each alphabet or a symbol or a digit etc., a code is pro and fixed. When a key is pressed, the code for the computer. Various types of coding are available for computers. But the most common  and popular code is ASCII which stands for American Standard Code for Information Interchange.

fact file – input unit converts the input feed by input devices into the binary (0.1) from which the  computer can understand quite easily  the are used for :

accepting data from the use into the computer system. 

accepting instructions from the users 

accepting commands for running , aborting or ignoring a progaram.

The Mouse


A mouse is a pointing device with a roller at its base. A mouse can be of different kinds.

We hold it in one hand and move across a flat surface. Its movement and the direction is detected by two rotating wheels on the underside of the mouse. The wheels have their axes at right angles to each other. Each wheel is connected to a shaft encodes which emits electrical pulses for every incremental movement to the wheel. The pulses transmitted by the mouse determines the cursor movement

facts – a mouse is used to draw sketches , diagram etc. on the crt screen.

An optical mouse uses a light emitting diode and photo diodes to detect movement relative to the underlying surface, rather than moving some of its parts – as in a mechanical mouse. 

A mouse’s sensor takes a continuous series of photographs of the surface, over which the mouse is moving. By comparing these pictures, the mouse’s process calculates, co-ordinates obviously, for optimum measurement and this results in perfection of the image. The first language co-ordination task is to illuminate the surface.

Until now, red LEDs were used to do that. The surface reflects the backlight, which is focused by lenses before it hits the sensor

fact file – a recent innovation by Logitech replaced the LED with a smaller laser .this laser creates a more concentrated beam and its light is more stable , producing a more detailed image .as in a CD or DVD player , lasers are  particularly effective for detecting surface irregularities 



A scanner is a device similar to a photocopier. A photocopier prints the given printed image/matter written on a paper. And a scanner creates an electronic form of the printed image, which can later be manipulated, changed and modified according to the requirements.

Types of scanners are as follows:

1. Handheld scanners
2. Flatbed scanner 
3. Drum scanner

FACT FILE – the scanner can convert any image into electronic from by shining light on to the intensity of the reflection at every point 

Optical Character Reader (OCR)

An optical character reader is used to read character of special type of font (or fonts) printed on conventional paper with conventional ink. The printed characters are examined by passing them under a strong light and a lens system, which differentiates light (no ink) from inked areas, and a logical system which attempts to determine which of the possible characters is being examined. The system in actual use depend heavily on the fact that only a limited number of characters in a particular font are used, but such systems are still quite useful. The ABCDEFGHIJKLMNOPQRSTUVWXYZ standard type font recommended by the ANSI optical character committee as in YSH$%&*{]-+:”..? figure.

Magnetic Ink Character Reader (MICR)

In this method, human readable characters are printed on documents (such as cheques) using a special magnetic ink. Special font has been set for these characters by American Banking Association. A magnetic ink character reader (MICR) reads these characters by examining their shapes, using a 7 x 10 matrix; it determines, from the response of the segments of the matrix to the magnetic head. This information is, thus, transmitted to the system. The determination of the character, which is read, is greatly facilitated by the Careful design of the characters and the use of the magnetic ink.

FACT file – micr is mostly used in banks in a cheque , for instance the branch code account number , and cheque number are preprinted at the bottom using magnetic inc . the amounts of the cheque is later entered by a clerk using a machine which prints the amounts with magnetic ink .  the cheque itself  can now be read using micr .

Light Pen

A light pen is also a pointing device. The light pen consists of a photocell mounted in a pen shaped tube. When the pen is brought in front of a picture element of the screen, it senses light coming from a limited field in view. The light coming from the screen causes the photocell to respond by generating a pulse. This electric response is transmitted to a processor that identifies the pixel (graphic point) the light pen is pointing to. Thus, to identify a specific location, the light pen is very useful. But the light pen provides no information when held over a blank part of the screen because it is a passive device with a sensor only.

The light pen is also used to draw images on the screen with the movement of the light pen over the screen, thus the lines are drawn.
Some other input devices like Trackball (which works similar to mouse), Joystick (which is generally used in games), Digital camera (which is used for video conferencing) and Microphone (which is used to input sound).

(II) Central Processing Unit (CPU)

The computer uses a microprocessor to do its work. The microprocessor, also known as CPU or central processing unit, is the brain of every computer. The central processing unit also contains the control unit, the arithmetic and logic unit, both working together as a team to process the computer’s commands. The arithmetic and logic unit (ALU) does all the computations. The control unit (CU) manages the flow of information within the various devices of the computer. Once the results are ready, they are sent to the output unit. A typical microprocessor adds, subtracts, compares two numbers and fetches numbers from one area to another. These operations are the result of a set of instructions (called programs) that are part of the microprocessor design. When the computer is turned on, the microprocessor is designed to get the first instruction from the basic input/output system (BIOS) that comes with the computer as part of its memory. After that, either the BIOS, or the operating system that BIOS loads into computer memory, or an application program “drives” the microprocessor giving it instructions to perform.

facts  – the first microprocessor was the intel 4004 introduced in 1971 . contained  2,300 transistors and performed about 60,000 calculations in a second . today ,s  microprocessor are packed with more than 5.5 million transistors and can perform hundreds of million of calculations every second. 

(III) The Output Unit

The Output unit is responsible for producing the output in user readable form. Various output devices like monitor (also called VDU i.e. visual display unit), printer, plotter, etc. make the output unit of a computer.
Mainly there are three principal devices to output information from a computer. These are printers, video terminals and computer output microfilms. Let us examine each of them individually.

fact file – the function of an output device is to represent processed data to the user the computer sends output to the monitor if the user needs to see the output . the output is sent to printer whenever the output is needed in hard copy (printed form ) . the sound output is produced with the help of speakers. 


A most convenient and useful method, by which the computer can deliver information, is by means of printed characters. The printed output is also known hard copy. Printers can be divided into two distinct categories:

1. Impact printers : In these printers, there is mechanical contact between the print-head and paper.

2. Non-impact printers : In these printers, there is no mechanical contact between the print-head and paper.

Impact Printers

The impact printer can be classified into following categories:

(a) Line Printer

(b) Character Printer

Line Printer

A line printer prints a complete line at a time. Printing speed varies from 150 lines to 2500 lines per/minute with 90 to 100 characters on 15 inch line.

Character Printer (Serial printer)

Character printer prints one character at a time, with the print head moving across a line. Serial printers normally print 30 to 300 characters per/sec. Broadly, serial printers may be divided into two categories.

(i) Dot matrix printers
(ii) Letter quality printers

A Dot Matrix Printer (DMP) is the most popular serial printer. In DMPs, the printing head contains a vertical array of pins. As the head moves across the paper, selected pins fire against an inked ribbon to form a pattern of data on the paper. The letter quality printers print full characters (continuous character not as the character made of dots). The most popular printer of such a type is daisy wheel printer. In a daisy wheel printer, its print-head resembles a daisy flower, with its print arms appearing like the petals of the flower. While printing, the character to be printed is sent to the printer buffer. The hub is continuously rotating at high speed, and a hammer strikes the appropriate character when it is in position.

fact file – there are two types of line printers these are drum printers and chain printers 

a drum printers consists of a cylindrical drum on which characters are embossed .

a chin printers  consists of a steel hand on which the characters are embossed  line printers are normally designed  for heavy printing applications and can print continuously for a few hours.     

Non-Impact Printers

The natural limitations of speed in electromechanical devices and cost considerations have led to the development of printer called non-impact printers. These printers can primarily be categorized as follows:

(i) Electromagnetic Printer : By using magnetic recording techniques, a magnetic image of what is to be printed, can be written on a drum surface. Then this surface is passed through magnetic powder which adheres to charged areas. The powder is pressed onto the paper.

(ii) Thermal Printer: An electric pulse can be converted to heat on selected sections of a printing head or on wires or ribbons. When this heat is applied to heat sensitive paper, a character is printed.

(iii) Electrostatic Printer: For electrostatic printers, the paper is coated with a non-conducting dielectric material which holds charges when voltages are applied with writing “rubs” heads. These heads write dots on the paper as it passes. Then the paper passes through a toner, which contains material with coloured particles carrying an opposite charge to that written by the nibs, as a result, particles adhere to the magnetized areas, forming printed characters.

(iv) Inkjet Printer: It directs a high velocity stream of ink toward the paper. The stream is deflected, generally by passing it through an electrostatic field such as that used to deflect beams. In oscilloscopes in some systems, the ink stream is broken into droplets by an ultrasonic transducer.
(v) Laser Printer : These printers make use of copier technologies. The desired output image is written on a copier drum with the help of a light beam controlled by a computer. With this, certain parts of the drum surface get electrically charged, then this drum surface is exposed to the laser beam. These laser exposed areas attract a toner that forms the image by attaching itself (toner ink) to the laser generated charges on the drum. The toner is, then, permanently fused on paper with hot roller with pressure

Visual Display Unit (VDU).

(Many applications require a graphical output apart from printed output. For example, Pie charts, Bar charts and Graphs with annotations are useful representation of information.) Plotters are the output devices that produce good quality drawing and graphs. There are two types of plotters drum plotter and flat bed plotter.


some  facts – in a drum plotter , the output paper is mounted on a rotating drum . a flat bed plotter consists of a stationary horizontal plotting surface on which paper is fixed. 

Visual Display Unit (VDU).

A monitor (the screen) is a box consisting of a CRT (Cathode Ray tube) and its power supply. The CRT operates much like those in television sets.

Liquid Crystal Display (LCD)

liquid crystal display (LCD)
liquid crystal display (LCD)

CRT screens are relatively heavy and bulky, and so they are not used on smaller portable computers. Rather, these notebook sized PCs are equipped with flat panel liquid crystal display (LCD) screen that operates like the small silver gray displays found on some digital watches and pocket calculators. A special liquid is sandwiched between two plates. The top plate is clear and the bottom plate is reflective. The molecules in this liquid are normally aligned so that light passes through to the bottom surface and reflects back out through the top plate.

File fact –  today most lcd cells produce dark image on a silver background but colour  lcd panels have been developed , and it is expected that the use of monochrome and colour lcd and display will grow rapidly 


Storage devices are one of the most important component of the computer system, Storage refers to the media and methods used to keep information available for later use Two types of storage devices are used in computers.
1. Primary storage
2. Secondary storage

classification of memory
classification of memory

primary storage 

often called main memory , primary is that part , which holds isstructions  and data for rapid and direct access by the computers central processing unit (CPU) . primary storage can be classified into (I)ROM (II) RAM 

Read Only Memory (ROM)

read only memory (rom)
read only memory (rom)

As its name implies, you can only read it. ROM is that part which stores instructions permanently in the computer. Only the computer manufacturer can provide these programs in ROM. Once done, you cannot change it nor put any of your own data or programs in ROM. All the software and operating system are placed in ROM.

Random Access Memory (RAM)

 random access memory (ram)
random access memory (ram)

Memory that we can both, read from and write to, is called RAM. RAM is the working memory. Data can be read (retrieved) or written (stored) in RAM; by providing the computer with an address location, where the data is stored or where you want it to be stored. When the data is no longer! required, you may simply write over it. Thus, you can use the storage location again and again.

fact file – a computer performance depends upon the power (speed) of its processor , the amount of ram and the speed of its hard drive 

Secondary Storage

Secondary storage, also called storage, is used to store data and programs when they are not being processed. Unlike primary storage, secondary storage is not directly accessible by the CPU. The computer usually uses the input and output devices to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage is necessary because you can store the data you have used or the information you have derived from processing. Further more, primary memory is limited in size, whereas secondary storage media can store as much data as necessary. The two main types of secondary storage are magnetic disks and optical disks. The following are examples of secondary storage units found in most computers.

Hard Disks

hard disks
hard disks

A hard disks is a device used for mass storage of data needed for direct access. It can be used to retrieve any record of data at a very fast speed. They consist of a number of disks with the read/write head sealed inside a pack. As hard disk is more stable, being rigid, its track and bit densities are much higher than those of a floppy disk. It stores more information at a faster rate as compared to a floppy disk. 

computer system

fact file – a hard disk capacity may range from 1 gb to 260 gb. the information stored on a hard disk can be read many times without erasing the stored data . the data stored for an indefinite preiod until erased .

Floppy Disk

A floppy disk is used to store the work done on a computer. You can save your work on a floppy disk and retrieve it whenever you want. It is made up of a thin and flexible plastic material. This thin plastic film is coated with a material known as iron oxide for recording the data.
The data is stored on floppy disk in a number of invisible concentric circles called as tracks. These tracks, like the rings of a tree, begin at the outer edge of the disk and continue towards the center without ever touching.
Each track has a designated number and each is divided radially into a number of regions called as sectors. Each tracks contains the same number of sectors.

CD-ROM Drive

The CD-ROM drive reads information stored on a Compact Disk. While floppies and hard disk are magnetic media, the CD-ROM is an optical media. The life span of optical media is much more than the magnetic media, which makes CD-ROM a very useful tool for storing data.
A CD-ROM can hold 640 MB of data. CD-ROM drives are usually installed inside the computer case.

facts  – the disk made up of a resin ,  such as polycarbonate. it is coated with a material which changes its reflecting property when a high intensity laser beam is focused on it . the coating material is highly reflective usually laser beam forms a tiny pit along a trace to represents 1 and the surface without a pit known as land represents 0.

Working of CD

 working of CD
working of CD

CD is a simple piece of plastic, 12 cm in diameter, about four-one hundredths (4/100) of an inch (1.2 mm) thick. Unlike the hard disk or floppy disk, there is only one track of data on the optical disk, circling from the inside of the disk to the outside, and all data are stored in a spiral. CDs store music and other files in digital form – that is the information on the disk is represented by a series of l’s and O’s. These 1’s and O’s are represented by millions of tiny bumps and flat areas on the disk reflective surface. The bumps and flats are arranged in a continuous track that measures about 0.5 microns millionths of a metre across and 5 km long.
The CD drive spins the disk while passing laser beam that is focused on the data side of the disk. When the laser passes over a flat area in the track, the beam is reflected directly to a special sensor on the laser assembly. The CD-player interprets this as a 1. When the beam passes over a bump, the light is bounced away from the sensor. The CD player recognizes this as a 0. 

computer system

DVD Drive

The digital versatile disks (DVD) are now widely used in computers and for home entertainment. They have now become a popular medium for storing information and videos. The DVD is almost similar to the CD. Its working is also similar to the working of the CD, but! it can hold a lot more information than the CD-about 4.7 (GB) (that’s seven times as much as a CD. DVDs can hold more data because the bumps are smaller and the tracks are closer together. computer system

 These are different types of CD-drives and DVD drives :

Drive TypeKnown AsFunction
Compact Disk Read only memory  CD-ROMRead CD-ROM and CD-R
Compact Disk RecordableCD-RReads CD-ROM and CD-R. Writes once on special disk name CD-R.
Compact Disk Re-writableCD-RWReads CD-ROM and CD-R. Writes and rewrite on special disk named CD-RW.
Digital Versatile Disk Read only memoryDVD-ROMReads all CD formats. Reads DVD -ROM. Reads and write DVD Disks
Digital Versatile Disk RewritableDVD-RWReads CD-ROM and DVD ROM. Writes CD-R, CD-RW and DVD.

USB Flash Drive

usb flash drive
usb flash drive

The USB flash drive is a small, portable data storage device integrated with a USB (Universal Serial Bus) connector. It acts as a portable hard drive and is easy to use as it is small enough to be carried in a pocket and can be plugged into any computer with a USB drive. USB flash drives also are called thumb drives, popularly known as pen drives or simply USB drives.  computer system


computer system

» A computer is an electronic device that can perform a variety of operations according to a set of instructions called program.
» Unprocessed raw facts and figures are known as data. >> Processed data, which conveys proper meaning, is called information.
> Computer functions through three phases—Input, process and output.
» Input unit (various input devices) is responsible for input phase i.e. it takes input from the user and forward it for processing. computer system
>> The central processing unit (CPU) is responsible for carrying out the processing.
> Output Unit (various output devices) is responsible for the output phase i.e. it makes available output to the users.
>> Various input devices are keyboard, mouse, scanner, bar code reader, OCR, MICR. light pen etc.
>> Various output devices are printer, plotter, speaker, monitor, LCD etc.
» Memory is the internal storage area, which holds the data and instruction during processing. computer system

computer system

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