Computer is an electronic device with a ability to: -



1. Accept data 2. Input, Store and execute instruction. 3. Perform mathematical and logical operation 4. Output results according to users requirement

Computer has certain Limitation:-

1. Cannot think on their own 2. Task has to be described in detail. 3. Do not learn from experience. 4. Cannot detect or correct errors in logic or data.

HISTORY OF THE COMPUTER : People have always needed to count. Earlier they counted with their fingers and probably through scratch making on trees or bones or on the walls of their caves. Over the centuries the science of numbers and computing has changed dramatically. People are now able to solve very sophisticated problems, and increasingly so with the aid of computers. Today we use computers in virtually every environment. From the executive in an office to the housewife and her washing machine to the teenager recording his/her favorite television programme, computers have entered into practically every sphere of human activity. The history of computing can be traced back to Abacus (2000 BC). Used primarily by merchants, the Abacus was a mechanical device used to add, subtract, multiply and divide numbers. Centuries later, mechanically operated devices were developed. These machines could add and subtract numbers (in 1642 Blaise Pascal's Calculating Machine), as well as multiply divide numbers (in 1671 Leibniz's Calculator) A few years later Charles Babbage, referred to as the "father of computers" devised a machine (Analytical Engine) which could be "programmed" by instructions coded initially on punched cards and then stored internally.

GENERATION OF COMPUTERS :

First Generation Computers - 1951-59 : They used vacuum Tubes as their principal component. They could store 10,000 to 20,000 characters. Magnetic Core Memory was used.

Second Generation Computers - 1959-64 : The Second Generation Computers replaced the Vacuum Tubes with Transistors. This led to the miniaturization of Computers. The concept of Multi Programming was introduced with Second Generation Computers. The most popular Second Generation Computer was the IBM 1401.

Third Generation Computers - 1964-70 : The Third Computers introduced integrated circuits, the equivalent of hundred and thousands of transistors on a small silicon chip. This drastically reduced the cost, size and power requirements. This technology produces powerful Mini Computers.

Fourth Generation Computers - 1970 till now The LSI (Large Size Integrated) Technology with many thousand of Electronic Devices on a small silicon chip signaled the Fourth Large Number of Character could be stored and also these Computers were much faster. IBM 370 was most popular machine.

A computer system can be viewed as a system of three Major Components:-

Hardware : It deals with a computer equipment that is mechanical, electrical, and electronic parts of the computer.

Software: It contains programs that instruct a computer how to process data and generate required information.

Human-ware : Person who operate the computer and also those who write the program i.e. - operator, programmers etc

CENTRAL PROCESSING UNIT :-

The heart of the computer is CPU It performs the various function with help of following components :-

1. RITHMETIC LOGICAL UNIT (ALU) :- Performs the actual calculations such as addition, multiplication, subtraction, and comparison like greater than lesser than, equal to, positive, negative or zero

2. MEMORY UNIT (MU) :- Memory unit or main storage unit holds data, instruction (that are being interpreted and executed, the results are ready for the output)

3. CONTROL UNIT (CU) :- The control unit co-ordinates the operation ofthe hardware. It also co-ordinate the flow and execution of data and instruction that are feed into the memory or main storage of CPU.

PERIPHERAL DEVICES

Peripheral devices can be classified as

1) INPUT DEVICES: - It allows feed the data into C.PU. (Computer) Examples of output devices are explained below: -

1) KEYBOARD - It is a important input device which is use every where. The keys are same as typewriter. They are classified as follows: -A) Alphabet Keys (A to Z). B) Numeric Key (0 to 9) C) Alphanumeric keys (!@#$% ~ &*) D) Function keys (Fl, F2, F3,..... F12) E) Arrow keys (Up arrow, Down arrow, Right arrow, Left arrow) F) Special keys (ENTER, TAB, CAPS LOCK, SHIFT, CTRL, ESC, ALT) 2) MOUSE - It is a device, which can easy to operate by one hand only.

It looks like a rat or mouse. It includes a three buttons & we can operate mouse through that buttons

2) OUTPUT DEVICES - The data, which we feed in computer through input device that data are displayed through, output device whenever called. Examples of output device as follows: -

1) Monitor (Screen of the computer)

2) Printer (DOT Matrix, Laser, etc.)

3) Backing Storage Devices :- Are those devices which can store data feed in by the use of input device. Some examples of backing storage devices are as below:-1) Hard Disk 2) Floppy Disk 3) Compact Disk (CD)

CLASSIFICATION OF COMPUTER

Computers can be classified on purpose, components and size

1.ANALOG COMPUTERS 2.DIGITAL COMPUTERS 3.HYBRID COMPUTERS

Analog Computers : Analog computers are computer that measures physical quantities (eg. Temperature, length, pressure, Whether reports etc...) and convert them to numeric values. It is used mainly for scientific & engineering purpose.

Digital Computers : Digital computers are used for mathematical operations such as (eg . addition ,subtraction, letters, symbols)

Hybrid Computers: The features of analog and digital computer are combined to create a hybrid computing system. The doctors to measure hearts beats SIZE mostly use hybrid computers –

All digital computer store numbers, letters and other characters in coded form. The code used to represent characters is the binary code - i.e. a code made up of binary digits or bits. Every character is represent by a string of "Os" and ""Is" - the only digits found in the binary numbering system. When data is types into a computer the keyboard convert each keystroke into a binary character code. This code is then transmitted to the computer, when the computer transmits the data to the - printer or the screen, or to the disk, each individual character is communicated in binary code. It is then converted back to the specific character while displaying or printing the data.

One 'Bit1 is a short of Binary Digit. A collection of 8 bits is known as a BYTE and half of byte i.e. a collection of 4 bits is known as a NIBBLE; 1 Byte= 8 Bits; 1 Kilobyte (KB)= 1024 Bytes; 1 Megabyte (MB)= 1024 KB; 1 Gigabyte (GB)= 1024 MB.

Note :- Every character you type occupies 1 byte, Every Space occupies 2 bytes and every Enter you hit occupies 2 bytes.

TYPES OF STORAGE SYSTEM

1. INTERNAL STORAGE :-

RAM :- (Random Access Memory ).Where programs arid data are held during processing temporarily. Data stored in the RAM is lost when either the machine is switched off. ROM :- (Read Only Memory). Where permanent instructions or data are held. The ROM does not require a continuous supply of power to retain it contents.

2. EXTERNAL STORAGE:-

(A) HARD DISK : Hard disks are a collection of/ pack of diskettes, known as platters, made of aluminum, with their surface being coated with iron oxide joined together to form a cylinder. They have more storage capacity and speed than floppy disks.

(B) Floppies are made of Mylar plastic coated with magnetic oxide. The flexible material is cut into circular pieces.5 1/4" or 3 1/2" in diameter. They are called Floppy disk"