DOS, the Disk Operating System

Turning the personal computer on is not enough; it must have instructions for the tasks it is to perform. These instructions come in the form of software. The primary tasks and functions the personal computer performs come from the instructions in systems programs.

You have already learned that there are specific systems software instructions embedded in chips that make up ROM (read only memory). These instructions help the computer give itself a checkup when you switch the power on, to make sure everything is in working order. Most of these instruc­tions occur without our being aware of them. However, one that you often can see when you first turn the power on is the computer checking its RAM.

The other aspect of systems software, the one we can actually interact with, is called the operating system. The operating system for the personal computer is called DOS,for disk operating system. DOS must be loaded into the personal computer's main memory before it can be used. There are also a number of instructions given to the computer by the operating system. Many are unavailable to you, the knowledge worker. One that is very important that you can't see is the Basic Input/ Output System (BIOS). It contains instructions specific to the computer you are using; for example, there is a BIOS that only works on an IBM PC.

When you load the operating system into the computer's memory, it is called a boot or booting the computer. The term comes from the old saying, "Pulling himself up by his own bootstraps," meaning someone who is able to do something on his own. Starting a program in the early days of computers was called bootstrapping, shortened to boot. Once booting is completed, you can issue DOS instructions and use application programs such as word processing.

DOS awakens the hardware and allows you to control the personal computer. It is responsible for managing all the input and output tasks, such as assuring that when you type a character on the keyboard, that same exact character appears on the screen and is stored in memory. Think of yourself as the personal computer's manager; DOS makes sure all your instructions are carried out accurately and promptly.