How Does a Computer Work?

Most activities follow the basic principle of Input-Process-Output. Consider an automobile assembly line. The raw materials required by an automobile assembling unit would include body, engine parts, tires, and so on.

These materials are forwarded to the assembling unit. This activity constitutes the input part of the cycle. The process is the actual building of the automobile. Therefore, the process acts upon what has been the input and produces the output, which in this case would be the finished automobile.

l-P-0 Cycle in an Automobile Manufacturing Unit

l-P-0 Cycle in an Automobile Manufacturing Unit

Like all other activities, a computer system too follows the Input-Process-Output or l-P-0 cycle. This can be best illustrated by an example of an airline reservation. A person who wishes to travel by air between Singapore and New York first has to fill in a request slip. This slip contains relevant data, i.e. details of name, age, place of destination, etc. The booking clerk keys in the data from the request slip into the computer. The process in this case includes examining the flight number, the date of the journey, the class requested, and determining whether seats are available as per the reservation details. The output of this process is some information confirming the booking, if seats are available. Otherwise, a message may be issued by the computer turning down the request.

Atlantis Airways

From: Singapore

To: New York



Date of Journey


Sally Chang


23rd November 1995



Example of Output in an l-P-0 Cycle

Now let us see how each component of the PC system is related to the l-P-0 cycle. The data in the request slip is input into the computer via the keyboard. Hence, the keyboard is an input device. The processing is performed by a component of the system unit called the microprocessor. The information regarding , availability of seats is displayed on the VDU. Hence, the VDU is an output device.

l-P-0 cycle components of a PC

The l-P-0 cycle components of a PC

The term hardware is used to refer to the physical components of a computer system. Thus, hardware comprises the input and output devices along with the system unit.