COMPUTER GENERATIONS:
ANATOMY OF COMPUTERS:
The
computer system consists of three units:
- Input device
- Central Processing Unit (CPU)
- Output device
Block diagram of a
Computer:
The
various functions of these units can be summarized as:
Unit Function:
1. Input device: Reads information from
input media and enters to the computer in a coded form
2. CPU
(a)
Memory unit: Stores program and data
(b)
Arithmetic Logic unit: Performs arithmetic and logical functions
(c)
Control Unit: Interprets program instructions and controls the input and output
devices
3.Output device: decodes information
and presents it to the user
Central Processing Unit: It is the part of the
computer that carries out the instructions of a computer program. It is the
unit that reads and executes program instructions. Hence it is known as the
brain of the computer. The CPU consists of storage or memory unit, Arithmetic
Logic Unit (ALU) and control unit.
(A).
Memory Unit: It is also known as the primary storage or main memory.
It stores data, program instructions, internal results and final output
temporarily before it is sent to an appropriate output Device. It consists of
thousands of cells called ―storage locations‖. These cells activate with
―off-on‖ or binary digits(0,1) mechanism. Thus a character either a letter or
numerical digit is stored as a string of (0,1) Binary digits ( BITS). These
bits are used to store instructions and data by their combinations.
(b)
Arithmetic and Logical Unit (ALU): It is
the unit where all Arithmetic operations (addition, subtraction etc.) and
logical functions such as true or false, male or female are performed. Once
data are fed into the main memory from input devices, they are held and
transferred as needed to ALU where processing takes place. No process occurs in
primary storage. Intermediate generated results in ALU
(c).Control
Unit : It acts as a central nervous system and ensures that the
information is stored correctly and the program instructions are followed in
proper sequence as well as the data are selected from the memory as necessary.
It also coordinates all the input and output devices of a system