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.

Managing Data and Software


Before looking into data and software management, let us find out what is disturbing Mr. Croft of Croft Constructions. He and his employees seem to be having problems using computers in their office. The problems are related to managing data and software. Here are the problems as described by them.

Croft: On Thursday, I employed Sally, and decided to put her to work on the computer immediately. As Betty was using one of the machines, I asked her to use the other. This machine did not have MS Word. So I took out the original diskettes and began to load MS Word. To my dismay, I found that the diskettes were corrupted. I called up my software dealer and got another copy the next day. This meant a day wasted for Sally.

Betty: Mr. Croft wanted a list of clients based in New York. I had been updating the database file on both machines and could not remember which machine I had worked on last. As a result, I had to manually check the files. A waste of time and effort. Further, Mr. Croft does not want information about his clients falling into unauthorized hands. I keep files containing client information only on floppy disks, which means unloading and loading the diskettes each time I want to update the files,

Sally: As I was typing a letter for Mr. Croft, I found the message, Your PC is now STONED!', displayed on the screen. As I did not know what it was, I ignored it. Later Mr. Croft discovered that it was a virus. We had to do a major cleaning operation to get rid of the infection.

The above situation highlights some common problems of data and software maintenance. These problems can be easily rectified by maintaining multiple copies of data and software, hiding files containing confidential information and protecting files from viruses. These and related issues will form the contents of this session.

Master and Working Copies of Data and Software

Smallville High School had a file containing the names and marks of its students. While working with the diskette, the Principal accidentally deleted all the files. The results of the students could not be given on time.

The above mentioned problem would not have arisen if the Principal had additional copies of the same set of files.

Consider another situation. Suppose you open a file which contains a letter. To make modifications to it, you will open it, modify it and save the modified letter in the same file. If the power fails when you are saving the file, there is a chance that the data will get damaged. A damaged file is called a corrupted file in computer jargon. Now you will have to write the letter again, unless you had made a copy of the letter earlier. An additional copy of a file is called a backup.

Most computer users keep two or three copies of the same file. The original copy of data/software is called the master copy and the duplicates you make are called working copies. Most users use only the working copy so that the original is always available for emergencies. For example, the master copy will be useful if your hard disk crashes (a hard disk is said to have crashed if all the data and software stored in it cannot be accessed) and your working copy gets corrupted. Or, take the case when you are using your data after a long time. If the duplicate is corrupted, either due to bad storage or maintenance problems, you can always use the master.

Backing up is the process of archiving data and software. Since the amount of data to be backed up is usually very large (sometimes in excess of 500 MB), backups are typically taken on storage mediums like CD-ROM, cartridge tapes and M-0 disks. Most operating systems provide facility for backing up data and software.

Windows NT provides a utility for backing up and restoring files from tape drives. Windows NT Backup is a graphical tool for protecting data from accidental loss or hardware or media failures. NT Backup makes it easy to use a tape drive to backup and restore important files on the system.