Input Unit: We need to first enter the data & instruction in the computer system,
before any computation begins. This task is accomplished by the input devices. (Eg:
keyboard, mouse, scanner, digital camera etc). This device is responsible for linking
the system with the external environment. The data accepted is in a human readable
form. The input device converts it into a computer readable form.
Storage Unit: The data & instruction that are entered have to be stored in the
computer. Similarly, the end results & the intermediate results also have to be stored
somewhere before being passed to the output unit. The storage unit provides solution
to all these issues. This storage unit is designed to save the initial data, the
intermediate result & the final result. This storage unit has 2 units: Primary storage
& Secondary storage.
Primary Storage: The primary storage, also called as the main memory, holds the
data when the computer is currently on. As soon as the system is switched off or
restarted, the information held in primary storage disappears (i.e. it is volatile in
nature). Moreover, the primary storage normally has a limited storage capacity,
because it is very expensive as it is made up of semiconductor devices.
Secondary Storage: The secondary storage, also called as the auxiliary storage,
handles the storage limitation & the volatile nature of the primary memory. It can
retain information even when the system is off. It is basically used for holding the
program instructions & data on which the computer is not working on currently, but
needs to process them later.
Central Processing Unit: Together the Control Unit & the Arithmetic Logic Unit
are called as the Central Processing Unit (CPU). The CPU is the brain of the
computer. Like in humans, the major decisions are taken by the brain itself & other
body parts function as directed by the brain. Similarly in a computer system, all the
major calculations & comparisons are made inside the CPU. The CPU is responsible
for activating & controlling the operation of other units of the computer system.
Arithmetic Logic Unit: The actual execution of the instructions (arithmetic or logical
operations) takes place over here. The data & instructions stored in the primary
storage are transferred as & when required. No processing is done in the primary
storage. Intermediate results that are generated in ALU are temporarily transferred
back to the primary storage, until needed later. Hence, data may move from the
primary storage to ALU & back again to storage, many times, before the processing
is done.
Control Unit: This unit controls the operations of all parts of the computer but does
not carry out any actual data processing.It is responsible for the transfer of data and
instructions among other units of the computer.It manages and coordinates all the
units of the system.It also communicates with Input/Output devices for transfer of
data or results from the storage units.