Computer Organisation :: 23
All data and instructions are stored here before and after
Intermediate results of processing are also stored here.
3. Processing: The task of performing operations like arithmetic
and logical operations is called processing. The Central Processing Unit (CPU) takes data and instructions from the storage unit
and makes all sorts of calculations based on the instructions
given and the type of data provided. The result is then sent back
to the storage unit.
4. Output: This is the process of producing results from the data
for getting useful information. The results could either be displayed on the screen or may be printed for future reference. The
output unit therefore allows the results to be either stored inside the computer for further processing or may give you the
results in human readable form.
5. Control: The process of input, output, processing and storage is
performed under the supervision of a unit called ‘Control Unit’.
It decides when to start receiving data, when to stop it, where to
store data, etc. It takes care of step-by-step processing of all
operations inside the computer.
2.4 FUNCTIONAL UNITS
In order to carry out the operations mentioned in the previous section the computer allocates the task between its various functional
units. The computer system is divided into three separate units for
its operation. These are 1) arithmetic logical unit, 2) control unit,
and 3) central processing unit.
(a) Arithmetic Logical Unit (ALU)
After you enter data through the input device it is stored in the
primary storage unit. Arithmetic Logical Unit performs the actual
processing of data and instruction. The major operations performed
by the ALU are addition, subtraction, multiplication, division, logic
and comparison. Data is transferred to ALU from storage unit when
required. After processing, the output is returned back to storage
unit for further processing or getting stored.
(b) Control Unit (CU)
The next component of computer is the Control Unit, which acts
like the supervisor seeing whether things are done in proper fash-