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) 1.First Generation Computers
Vacuum tubes were used which produce more heat
Speed of computing was measured in milliseconds
Limited storage capacityM
punched cards were used for I/O operation
2. Second – Generation Computers
Transistors and diodes were used.
Speed of computing was measured in microseconds
Consider about reduction of heat
Remarkable improvement in reliability
Storage capacity was increased
Magnetic tapes were used instead of punching cards.
3. Third Generation Computers
Integrated Circuits were used.
Speed is measured in nanoseconds
Occupied less space.
devices like visual display unit for I/O devices
4. Fourth – Generation Computers
Use of micro processor chip
Speed was measured in nano and picoseconds
Occupied less space
Commonly available as personal computers
Mini & micro Computers are developed from micro-processor
5. Fifth – Generation Computers:
Use of super large-scale integration (SLSI) chip in computer (super computers)
Capable of performing millions of instructions per seconds (MIPS)
Processing speed is high.
Use of RICS (reduced instructions set computing) for processing
Super computers are expensive.
Types of 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
4bits = 1 Nibble
8bits = 1 byte
1024 bytes = 1k or 1kb (kilobyte)
1024KB = 1MB (mega byte)
1024MB = 1GB (Gega byte)
1024GB = 1TBC Terabytes
Organization of Computer:
Arithmetic and Logical 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.
ALU (Arithmetic Logic Unit)
CU (Control Unit)
MU (Memory Unit)
1. 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.
2. 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)
3. ALU Consists of CKTs for arithmetic operations(+,-,*,/) and logical operations
Connected components of CPU are called peripherals Input devices
3. Dot Matrix Printer
4. Laser printers
5.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
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 program
Source Program Eg : ADD A, B, R, More R,S
Assembler Translated by Assemble
Object Program 0101 10101010
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
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.
Development of “C” (Introduction and history)
“C” is a programming language developed at AT & T Bell Laboratories of USA in
1972. It was developed Dennis Ritche in late 1970‟s. it began to replace the more familiar
languages of that time like PL/1, ALGOL etc.
“C” became popular because of its reliability, simple and easy to use
It was friendly capable and reliable
ALGOL 60 was developed and did not become popular because it was too general
and too abstract.
They developed “CPU” (Combined Programming Language)
Next as it could not come up to make ALGOL 60 better one they moved to
“BCPL” (Basic Combines Programming Language. Developed by martin Richard
At the same time a language called “B” written by ken Thompson at AT & T‟S.
Bell laboaratories as a further simplification of BCPL.
“C” s compactness and coherence is mainly due to it‟s one man language. ExLISP, AASCA
too general, too abstract
Hard to Learn & implementation
could deal only special problem
could deal only special problem
AT & T
Lost Generality of BCPL, B restored
Note : C is a middle level language because it was due to have both a relatively good
programming efficiency and relativity good machine effecience.