7 Computer programs
Earlier on I indicated that in order for a processor to perform a defined function it needs to be supplied with a list of instructions called a program. In this section I shall explore this idea a little further.
Software can be split into two categories, application software and operating systems. Application software is the name given to programs which enable a computer to perform specific tasks. The program that processes the image in the digital camera is one example; a word processor running on a PC is another.
In computers that are running several application programs, the programs may well be sharing some of the computer's resources, such as its display or its hard disk. If this is the case then an operating system provides general-purpose software that controls the sharing of resources amongst the various programs, making sure that they are not competing for the same resource. The operating system on a PC makes it possible for, say, information about incoming email to appear on the screen whilst a word processor is running and a document is printing. The operating system you are most likely to be familiar with is Windows® the computing requirements for this course specify that you must have access to a PC running a Windows® operating system.
Very simple computers, such as the one in the kitchen scales, have only one program running and consist of a modest set of resources. In such simple systems the distinction between the operating system and the application program is not clearly defined, and it is not customary to distinguish between them. But in more complex computers an operating system becomes useful, and in something as complex as a PC it is a crucial component.
In Section 7.2 I will look a little more closely at operating systems. Then in Sections 7.3 and 7.4 I will look at how application programs are developed.