A computer is an electronic device capable of manipulating numbers and symbols under the control of a set of instructions known as computer program. They are different stages of computers (generation)


First Generation Computers :

  1. Vacuum tubes were used which produce more heat
  2. Speed of computing was measured in milliseconds
  3. Limited storage capacity
  4. Punched cards were used for I/O operation

Second-Generation Computers :

  1. Transistors and diodes were used.
  2. Speed of computing was measured in microseconds
  3. Consider about reduction of heat
  4. Remarkable improvement in reliability
  5. Storage capacity was increased
  6. Magnetic tapes were used instead of punching cards.

Third Generation Computers :

  1. Integrated Circuits were used.
  2. Speed is measured in nanoseconds
  3. Occupied less space.
  4. Devices like visual display unit for I/O devices

Fourth-Generation Computers :

  1. Use of micro processor chip
  2. Speed was measured in nano and picoseconds
  3. Occupied less space
  4. Commonly available as personal computers
  5. Mini & micro Computers are developed from micro-processor

Fifth- Generation Computers :

  1. Use of super large-scale integration (SLSI) chip in computer (super computers)
  2. Capable of performing millions of instructions per seconds (MIPS)
  3. Processing speed is high.
  4. Use of RICS (reduced instructions set computing) for processing
  5. Super computers are expensive.

Types of Computers :

  1. Mainframe Computers
  2. Mini Computers
  3. Micro Computers
  4. Super Computers

Mainframe Computers work at a high speed, and have a high storage capacity Mini Computers are medium and powerful Computers. Micro Computer are the commonly used as general purpose Computer Data Storage in a Computer

  1. 4bits = 1 Nibble
  2. 8bits = 1 byte
  3. 1024 bytes = 1k or 1kb (kilobyte)
  4. 1024KB = 1MB (mega byte)
  5. 1024MB = 1GB (Gega byte)
  6. 1024GB = 1TBC Terabytes

Organization of Computer :

  1. Arithmetic and Logical unit
  2. Memory unit
  3. Control unit
  4. Input unit
  5. Output unit

The Input and Output units are used to receive and display Inputs & Solutions Common i/p & o/p devices : Keyboard, mouse, monitor, printer The CPU (Central Processing Unit) Consists of.


  1. ALU (Arithmetic Logic Unit)
  2. CU (Control Unit)
  3. MU (Memory Unit)

The Control Unit Controls all the activities of the Computer. It sends commands and control signals and finds the sequence of instruction to be executed. Memory Unit is the place where all input data and results are stored. Computer memory is also available in the form of Random Access Memory (RAM) ALU Consists of CKTs for arithmetic operations(+,-,*,/) and logical operations (<,>,>=,<=,==,!=)

Connected components of CPU are called peripherals Input devices Output devices Keyboard, Printer, Mouse, Monitor, Joystic, Dot Matrix Printer, Laser printers, LCD


Storage Devices :
  1. Floppy disk
  2. Hard disk
  3. Compact disk

Computer Main Memory :

Primary memory RAM (Random Access memory) Secondary memory ROM (Read only memory) Hard disk RAM : It is a temporary storage medium in a computer. The data to be processed by the computer are transferred from a storage devices or a keyboard to RAM results from a executed program are also stored in RAM. The data stored will be erased when the computer is off. ROM (Read only Memory) : This is a non-volatile or data storage medium which stores start up programs (operating systems).

This essentially stores the BIOS (Basic Input Operating System) Note : Basically Computer System components communicate it binaries as (0‟s & 1‟s, 0 refers OFF state,1 refer ON state) Languages of different Generation Computer.


First-Generation Language :

All the instructions are in the binary form and are referred to as machine level or low level language (LLL). It is very difficult to read the instructions written in binary Eg : 00110101011101110001, 101100001010101


Second-Generation Language :

All the instruction are in the forms of mnemonics. The symbolic instruction language called as Assembly Language. All the symbolic instructions are converted into binaries with the help of translator called Assembles. ASCII (American Standard Code For Information Interchange) is commonly used for translation of source Program into object Source Program Eg : ADD A, B, R, More R,S Assembler Translated by Assemble Object Program 0101 10101010 0100 00001101


Third-Generation Language :

These are written in English with symbols and digits. Then are known as High level language (HLL). common high level languages are c,c++, COBOL, BASIC, FORTRAN, PASCAL, etc. For execution the program is translation into binary form by compiler or interpreter. Source program Compiler, Object Prog, Linker, Executable Program Run the


Fourth-Generation Language (4GL"s) :

is a programming language or programming environment designed with a specific purpose in mind, such as the development of commercial business software. In the history of computer science, the 4GL followed the 3GL in an upward trend toward higher abstraction and statement power. The 4GL was followed by efforts to define and use a 5GL.

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