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10th March 2002

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Gresha & Avril
Gresha & Avril
Contents

COS: We can't do without it

We have talked about Windows XP and Linux in the past, but this week I thought of talking about Computer Operating Systems in general. The operating system defines our computing experience. It's the first thing we see when we turn on the computer, and the last thing we see before shutting it down. It's the software that enables all the programs we use. The operating system organizes and controls the hardware on our machines, yet most users can't say with any certainty precisely what it is that the operating system does. We'll tell you what a piece of software must do for that to be called an operating system, and show you how the operating system works.

It's should be clear that not all computers have operating systems. Your calculator, for example, doesn't need an operating system. It has one set of relatively simple tasks to perform, very simple input and output methods (a keypad and an LCD screen), and simple, never-changing hardware to control. Instead, the calculator simply runs a single program all the time.

For computer systems that go beyond the complexity of calculators, an operating system is the key to greater operating efficiency and easier application development. All desktop computers have operating systems. The most common are the Windows, UNIX and Macintosh operating systems. There are hundreds of other operating systems available that serve specialized purposes.

At the simplest level, an operating system does two things: It manages the hardware and software resources of the computer system. These resources include such things as the processor, memory, disk space, etc. On the other hand it provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.Managing the hardware and software resources is very important, as various programs and input methods compete for processing (CPU) time and demand memory, storage and input/output (I/O) bandwidth for their own purposes. The operating system makes sure that each application gets the necessary resources managing the limited capacity of the system as efficiently as possible.The second task, providing a consistent application interface, is important if there is to be more than one type of computer using the operating system, or if the hardware making up the computer is ever open to change. An application program interface (API) allows a software developer to write an application on one computer and to know that it will run on another computer of the same type, even if the amount of memory or the quantity of storage is different on the two machines. Even if a computer is unique, an operating system ensures that applications continue to run when hardware upgrades and updates occur, because the operating system and not the application is charged with managing the hardware and the distribution of its resources. Windows 98 is a great example of the flexibility an operating system provides. It runs on hardware from thousands of vendors. It can accommodate thousands of different peripherals in any possible combination.Within the family of operating systems, there are four types, categorized based on the types of computers they control and the sort of applications they support. The broad categories are: Real-time operating systems (RTOS) - they are used to control machinery, scientific instruments and industrial systems. They have 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. Windows and the MacOS 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-tasking 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 here 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 the remote user logins the network enables are, in the overall plan of the operating system, a program being run by the administrative user.
Now that we know the different types of operating systems and their functions, next time we will look into what happens when you turn on the power switch of your computer. So until then, celebrate life everyone!



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