by Kewoni Berkley

Created on: June 02, 2008   Last Updated: August 30, 2011

What is an operating system?

All computers require a host, a program which is used to interact with the user by providing a graphical user interface or command based interaction. The computer is useless without the operating system. It is the first program loaded onto the computer as it is started. The most common operating systems used are Microsoft windows, Mac OS X, LINUX or UNIX.

The operating system is responsible for managing the sharing of resources of the computer and programmers are able to access those resources. Also, it provides consistent harmony with hardware without having to know all the details about it.

On the computer, the first task performed by the operating system is the Central Processing Unit (CPU) which programs need to compete for attention. Thus the CPU is expected ensure every application get the necessary resources to run smoothly with other applications.

Secondly, there is the need for a consistent application interface. This is necessary so different types of computers can run the operating system similarly. The Application Program Interface (API) thus allows programmers to create program which have a homogeneous interface which makes the operating system easier to use.

The operating system, also allows for multiprocessing, so more than one processors can be supported and maintained. There is also multitasking where many program are run together. Operating systems are made, to handle multiple processes simultaneously. This is why a media player can be running while you are on the internet or typing up a text document. There are several methods which an operating system can use to perform multiprocessing.

Multiprocessing can be either symmetric or asymmetric. Symmetric processing is done by more than one CPU. Processes are designated to one CPU for processing one section of data while the other does the same simultaneously. This is the most common form of multiprocessing. Asymmetric is the case where only one processor carries out system tasks while the others process application programs. This can result in poor performance at times when many system tasks need to be processed.

In order for processing to occur, there is the need for multiprocessing protocol. This dictates how the processors and chipset will talk to each other to implement symmetric processing. An example of such protocol is APIC which is used on Intel chipset.

The first method which can be used, is time sharing. With this, it may seem like more than one programs are running together but in reality, each program is being processed one after the other. Even when a user has no programs running, the operating system has processes which must be carried out. So even here processes must be carried out simultaneously. What happens is that the processor allows each program a certain amount of time for each process.

Since the computer works at extreme speeds it can seem to humans that programs can run together harmoniously.

Another method is inter-processor communication. With this method, there are two CPUs on the system and they both work together to process data. Both processors share a common RAM. Virtual memory is used to store data; one CPU did this. The other CPU is responsible for reading the information off of virtual memory and output it. Again, since the computer con operate at extreme speeds it seems as though the CPU is running multiple program at the same time.

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