Within the broad
family of operating systems, there are generally four types, categorized based
on the types of computers they control and the sort of applications they
support. The categories are:
·
Real-time
operating system (RTOS) - Real-time
operating systems are used to control machinery, scientific instruments and
industrial systems. An RTOS typically has very little user-interface
capability, and no end-user utilities, since the system will be a "sealed
box" when delivered for use. A very important part of an RTOS is managing
the resources of the computer so that a particular operation executes in
precisely the same amount of time, every time it occurs. In a complex machine,
having a part move more quickly just because system resources are available may
be just as catastrophic as having it not move at all because the system is
busy.
·
Single-user,
single task - As the name
implies, this operating system is designed to manage the computer so that one
user can effectively do one thing at a time. The Palm OS for Palm handheld
computers is a good example of a modern single-user, single-task operating
system.
·
Single-user,
multi-tasking - This is the
type of operating system most people use on their desktop and laptop computers
today. Microsoft's Windows and Apple's MacOS platforms are both examples of
operating systems that will let a single user have several programs in
operation at the same time. For example, it's entirely possible for a Windows
user to be writing a note in a word processor while downloading a file from the
Internet while printing the text of an e-mail message.
·
Multi-user - A multi-user operating system allows
many different users to take advantage of the computer's resources
simultaneously. The operating system must make sure that the requirements of
the various users are balanced, and that each of the programs they are using
has sufficient and separate resources so that a problem with one user doesn't
affect the entire community of users. UNIX, VMS and mainframe operating
systems, such as MVS, are examples of multi-user operating systems.
It's important to
differentiate between multi-user operating systems and single-user operating
systems that support networking. Windows 2000 and Novell Netware can each
support hundreds or thousands of networked users, but the operating systems
themselves aren't true multi-user operating systems. The system
administrator is the only "user" for Windows 2000 or
Netware. The network support and all of the remote user logins the network
enables are, in the overall plan of the operating system, a program being run
by the administrative user.
With the different
types of operating systems in mind, it's time to look at the basic functions
provided by an operating system.
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