OPERATING SYSTEM 

A program that every computer seems to need. Your computer has one. The only 
part of it you usually are aware of is a file called COMMAND.COM (on a
computer with DOS), or CMD.EXE (on a computer with OS/2). The operating 
system is always there even though you don't see it. The most visible thing 
it does is print the prompt or display a new window to indicate it is ready 
for another command. It also does a lot of things that you don't see, like 
controlling the disk and printer.

Sometimes the operating system responds directly to your commands, sometimes 
it uses other programs to respond to them. When it uses another program to 
respond to your command, it will use the directories on your disks to find 
the program.
