A
computer is a programmable device and has its own architecture. This architecture
consists of three main functional units, namely:
·
Input
unit
·
System
Unit
·
Output
Unit
CPU:
Central Processing Unit CU: Control Unit
ALU:
Arithmetic & Logical Unit MU:
Memory Unit
Fig 02: Block Diagram of Computer
Input Unit
·
It
is an external device that is connected to the CPU.
·
It
is used to feed data and instructions for solving the problem at hand.
·
The
control unit sends signal to this unit to receive data and instructions from
the user, which is communicated to the CPU.
·
Examples: Keyboard, Mouse, Joystick, Scanner,
Trackball, Light Pen, Touch screen, Touch pad, Bar code reader, Microphone,
etc.
Output Unit
·
This
is used to display the result obtained after execution of a program.
·
Whenever
the user wants the output from the computer, the control unit sends signal to
this unit to be ready to accept processed data from memory and display it.
·
Examples: Monitor, Printer, Scanner, Plotter, Speaker, Headphones,
Fax, etc.
·
The
data and instructions obtained from input unit are processed by the system
unit.
·
It
is regarded as the brain of the computer and it provides the fundamental
commands and instructions for the working of the computer.
·
It
is sub-divided into two:
o
CPU
(Central Processing Unit)
§ CPU
fetches program instructions from RAM (input), interprets and processes it
(execution) and then sends back the computed results so that the relevant
components can carry out the instructions.
§ It is
further divided into two components:
·
ALU (Arithmetic & Logical Unit)
o
All calculations are carried out in the ALU.
o
It consists of electronic circuitry which performs the basic
arithmetic operations like +, -, *, /.
o
It also consists of electronic circuitry that performs logical
operations are gives us results in the form of true or false.
·
CU (Control Unit)
o
It controls and co-ordinates the activities of all the units of a
computer system.
o
It acts as the central nervous system of the computer.
o
It controls and times signals to various units to co-ordinate for
the specific operation.
o
MU
(Memory Unit)
§ This is a
storage device of the computer.
§ It stores the
data and instructions fed by the user and also the result which is produced after
processing the same data.
§ There are two
types of memory, one is called volatile memory and the other is non-volatile
memory.
In volatile
memory, information is retained as long as power is supplied to the chips. In non-volatile
memory, information is retained, even though power is not supplied.
Ø CPU Registers
o
A register is a small amount of storage available as part of a digital processor, such as a CPU.
o
They can be accessed
more quickly.
o
Computers load data
from a larger memory into registers where it is used for calculations,
manipulations, or tested, by some machine instruction.
Ø Main Memory
o
RAM
(Random Access Memory)
§ It is a
temporary storage medium in a computer.
§ All data to be
processed by the computer are transferred from a storage device or keyboard to
RAM during data processing. Results obtained from executing any program are
also stored in RAM.
§ RAM is a
volatile memory.
o
Cache
Memory
§ The
internal processing speed of a computer is very fast compared to the reading
and writing from/to disk. During the time of reading from disk the CPU is idle.
To reduce this waiting time and increase the processing speed, a cache memory
is used in the computer.
§ Cache
memory is a part of RAM that holds the data, which is needed next by the CPU.
§ The size of
cache memory is 512 KB.
o
ROM
(Read Only Memory)
§ Read
Only Memory is a permanent storage medium which stores start up programs. These
programs which are loaded when computer is switched on.
§ ROM
stores essentially the BIOS (Basic Input Output System) programs which are
recorded by the manufacturer of the computer system.
§ ROM
is non-volatile memory.
Ø Secondary Memory
o
This
is a permanent memory.
o
It
stores large amount of information for a long time
o
It
is also called backup memory or auxiliary memory.
o
It
is connected to CPU.
o
Examples: Hard disk, Floppy disk, CD, DVD,
Magnetic Tape, Flash memory, Jump drive, Pen drive, Cloud storage etc.
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