Information Systems Theory
Chapter 8: Operating Systems and System Software
This chapter discusses operating systems. The objectives important to
this chapter are:
- Understanding categories of system software
- Understanding operating systems
- Understanding transmission media
- Understanding the terms proprietary and portable
- Recognizing some major operating systems
As with the previous chapter, I will concentrate here on the most important
features of the chapter.
System software is defined on page 8.2 as software "related
to controlling the operations of the computer hardware". To the beginner,
that sounds like a definition of all software. By now you should have
an idea that some programs, like applications, only deal with their
own concerns (such as processing data into a report). Such programs must
interface with the system software to save files, to print,
to display data, and to perform any other function involving hardware.
The text discusses operating systems in terms of the interfaces they
offer to users:
- command line interface - user must type commands
- menu-driven interface - user may choose options from menus,
usually with a keyboard
- graphical user interface - user may use a mouse to click buttons
The menu-driven interfaces often allow a user to enter typed commands.
The graphical interfaces often allow the user to user menus and typed
commands as well.
A discussion of process management begins on page 8.4. A process
is a single task a computer is trying to fulfill. Computer operating
systems can approach tasks in a number of ways. Two broad categories are:
- single tasking - the operating system can only do one thing
at a time
- multitasking - the operating system loads more than
one task at a time. Often, this is an illusion. In cooperative
multitasking, several tasks are loaded into memory and the processor
give a few nanoseconds to each one in turn until they
are done. In preemptive multitasking, the same thing happens,
except that more important tasks are given more time than less important
Multiprocessing is mentioned on page 8.6. An operating system
that supports multiple processors can do real multitasking,
assigning different tasks to different processors.
You should be aware that an operating system must manage the memory
of a system as well as the input and output of a system.
The methods for doing so are beyond the scope of this class.
Two important measures of system performance are discussed
on page 8.10:
- response time - the time it takes from the moment a user enters
a request until the system responds with output to the
user. Some requests take longer than others, but measuring the same
request on different systems gives us a common ground to compare those
- CPU utilization - a measure of how busy the processor is on
a system. As I type this text, my processor is varying from 0 to 9 per
cent utilization (as measured by a utility in my operating system).
This is not much of a load. A processor that stays near 100 per cent
utilization is too busy to do anything else for a user.
An operating system may provide some security features, such
as asking a user for their name and password. This is more
common on network operating systems, however, desktop operating systems
can provide the feature as well.
A discussion of the processes that occur when loading an operating
system appears on pages 8.12 and 8.13. This does not mean when "installing"
the system; the information refers to the load that takes place
when you turn on the computer. This information is helpful when
diagnosing a problem that is happening during the execution of these processes.
Another concept is offered on page 8.14. Operating systems can be thought
of as either proprietary or portable. A proprietary
operating system only works on one kind of equipment, while a portable
operating system may be used on several types of computers.
A brief discussion of several operating systems follows. You
will want know something about most of them, since an operating system
is choice you make when purchasing a computer:
- DOS - stands for Disk Operating System. Several versions have
existed, from various vendors, notably Microsoft and IBM. This is an
older system that does not support a 32 bit graphic environment.
- Windows 3.x - this refers to versions 3.0, 3.1 and 3.11 of
Windows. These products were not really operating systems. They were
actually interfaces to the DOS operating system.
- Windows 95 - this version of Windows is more of an operating
system, but it is still an interface because it requires some DOS components
be loaded before it is loaded.
- Windows 98 - this version of Windows is a bit less reliant
on DOS than Windows 95, but again, it is not truly an operating system.
- Windows CE - this is a true operating system, but it is meant
for handheld devices, not desktop or laptop computers. Microsoft recently
(April, 2000) released version 3 of this system.
- Windows NT - this is the first version of Windows that is
truly an operating system for desktops, laptops, and servers. Its successor
is Windows 2000.
- Macintosh - a proprietary system, because it has only been
used on Apple Macintosh computers for most of its life. Several
versions have been released.
- OS/2 - an IBM product, this system can be run on many kinds
of machines. It is not a marketing success.
- UNIX - various versions exist. The original was invented at
Bell Labs. Many people are promoting one version or another as a replacement
- NetWare - this is a network operating system created by Novell.
The operating system runs on servers, a client interface runs on workstations
in the network. It is a widely used system, and it supports workstations
that run any of the operating systems listed above.