Operating
Systems Introduction
Author: Brian Brown, 1995-2000. All rights reserved.
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SECTION ONE : Part 2
What is a single-user operating
system?
We are all familiar with the concept of sitting down at a
computer system and writing documents or performing some task
such as writing a letter. In this instance there is one keyboard
and one monitor that you interact with.
| Operating systems such as Windows 95,
Windows NT Workstation and Windows 2000 professional are
essentially single user operating systems. They provide you the capability to perform tasks on the computer system such as writing programs and documents, printing and accessing files. |
 |
Consider a typical home computer. There is a single keyboard and mouse that accept input commands, and a single monitor to display information output. There may also be a printer for the printing of documents and images.
In essence, a single-user operating system provides access to the computer system by a single user at a time. If another user needs access to the computer system, they must wait till the current user finishes what they are doing and leaves.
Students in computer labs at colleges or University often experience this. You might also have experienced this at home, where you want to use the computer but someone else is currently using it. You have to wait for them to finish before you can use the computer system.
What is a multi-user operating system?
A multi-user operating system lets more than one user access the
computer system at one time. Access to the computer system is
normally provided via a network, so that users access the
computer remotely using a terminal or other computer.
| In the early days of large multi-user computers, multiple terminals (keyboards and associated monitors) were provided. These terminals sent their commands to the main multi-user computer for processing, and the results were then displayed on the associated terminal monitor screen. Terminals were hard-wired directly to the multi-user computer system. |  |
Today, these terminals are generally personal computers and use a network to send and receive information to the multi-user computer system. Examples of multi-user operating systems are UNIX, Linux (a UNIX clone) and mainframes such as the IBM AS400.
The operating system for a large multi-user computer system with many terminals is much more complex than a single-user operating system. It must manage and run all user requests, ensuring they do not interfere with each other. Devices that are serial in nature (devices which can only be used by one user at a time, like printers and disks) must be shared amongst all those requesting them (so that all the output documents are not jumbled up). If each user tried to send their document to the printer at the same time, the end result would be garbage. Instead, documents are sent to a queue, and each document is printed in its entirety before the next document to be printed is retrieved from the queue. When you wait inline at the cafeteria to be served you are in a queue. Imagine that all the people in the queue are documents waiting to be printed and the cashier at the end of the queue is the printer.
Operating system utilities
The operating system consists of hundreds of thousands of lines
of program instructions and these are stored on hard disk of the
computer. Portions of the operating system are loaded into
computer system memory (RAM) when needed.
To manage the computer system, users, printers, files and write
programs, the operating system is generally provided with a
number of utility programs. The utilities are used for
Operating System Interfaces
In addition, the operating system provides each user with an
interface that accepts, interprets and executes user commands or
programs. This interface is commonly called a SHELL or command
line interpreter (CLI). In some systems this might be a simple
text mode line-by-line entry using keywords (such as MSDOS or
UNIX), in other systems it might be highly graphical using
windows and a pointing device such as a mouse (such as
X-Windows).
Advantages and problems of multi-user
operating systems
The advantage of having a multi-user operating system is that
normally the hardware is very expensive, and it lets a number of
users share this expensive resource. This means the cost is
divided amongst the users. It also makes better use of the
resources. Since the resources are shared, they are more likely
to be in use than sitting idle being unproductive.
One problem with multi-user computer systems is that as more users access it, the performance becomes slower and slower. Another disadvantage is the cost of hardware, as a multi-user operating system requires a lot of disk space and memory. In addition, the actual software for multi-user operating systems tend to cost more than single-user operating systems.
What is a multi-tasking operating
system?
A multi-tasking operating system provides the ability to run more
than one program at once. For example, a user could be running a
word processing package, printing a document, copying files to
the floppy disk and backing up selected files to a tape unit.
Each of these tasks the user is doing appears to be running at
the same time.
A multi-tasking operating system has the advantage of letting the user run more than one task at once, so this leads to increased productivity. The disadvantage is that more programs that are run by the user, the more memory that is required.
What is software and what is application
software?
Software is just another name for program. We
often use the term to refer to a group of programs. For example,
you might get asked the question "what sort of software do
you have?". In this case, the person is asking you what
types of software do you have, and how many different software
programs do you have. I guess you could think of someone asking a
snake collector the question "What sort of snakes do you
have?". For the snake collector, they obviously have many
different types and sometimes several of the same species.
Software is similar. So you might respond to such a question by
answering that you have some word processing software such as
Microsoft Word and some games such as Quake and Sim City.
Application software excludes the operating system and those programs that are part of the operating system. In general, you buy application software for your computer. An example might be a word processor or a reference atlas.
What are general categories of application
software?
In general, software is divided into a number of
general categories.
Business Business software allows users to perform tasks related to running a business, such as paying accounts, keeping track of goods and items for sale, inventory software and writing reports. Examples of business software are Microsoft Works and Lotus Notes.
Education Education software is designed to teach or educate users. These include encylodedias, reference books and instructional programs. Examples of education software are Encylopedia Britannica and Microsoft Magic School Bus.
Entertainment/Games Entertainment software is designed for you to have fun with! Its purpose is to keep you entertained! This includes games software. Examples of entertainment software are Microsoft Age of Empires and Sim City 2000.
Utility Utility software is designed for you to perform routine tasks associated with the storage and manipulation of your information. This includes software such as schedulers, clocks, media players and communication tools. Examples of utility software are McAfee Virus Scan and Arcada backup software.
Revision Exercise 1
List FOUR things an operating system does.
List THREE home appliance devices in your home that probably have an operating system controlling their function.
List FOUR hardware devices on a typical home computer that an operating system has to initialize when it is turned on.
List THREE possible errors that might occur in a typical home computer that an operating system has to handle.
State THREE possible basic routines an operating system might provide for handling a hardware device.
