Inside your computer, there are many hardware components and peripherals. To control all of these pieces of equipment, we use an operating system. An operating system handles the dirty work, so-to-speak. It is the interface that allows users to interact with hardware.

Operating systems also handle programs. It takes instructions of a program controls the appropriate hardware.

There are many types of operating systems. The most popular ones include Windows 95/98, DOS, Linux, and the MacOS for the Macintosh. Because the operating system directly controls the components of the computers, operating systems written for one type of chip configuration may not work for another. For example, DOS will run on an Intel chip based computer, but not on a PowerPC Macintosh.

There are two types of operating systems in terms of users. They are multi-user and single-user.

Multi-user allows for the simultaneous use of an operating system by more than one person. By contrast, single-user operating systems allow for only one access at a time. Examples include Windows NT for multi-user and Windows 3.x or DOS for single-user.

Operating systems are also catagorized as single-tasking or multi-tasking. This is simply a distinction that denotes how many programs an OS can run at one time. DOS, for example, is a single-tasking environment. Windows, however, is multi-tasking.

There are also stand-alone systems and distributed systems. Stand-alone systems are systems where all the work is done in one place by one computer. In contrast, a distributed system spreads the work around through different systems seamlessly so the end user does not even notice this division of work.

DEFINITIONS:

operating system

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

Operating systems can be classified as follows:

· multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.
· multiprocessing : Supports running a program on more than one CPU.
· multitasking : Allows more than one program to run concurrently.
· multithreading : Allows different parts of a single program to run concurrently.
· real-time real_time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.

As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.

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batch processing

Executing a series of noninteractive jobs all at one time. The term originated in the days when users entered programs on punch cards. They would give a batch of these programmed cards to the system operator, who would feed them into the computer.

Usually, batch jobs are stored up during working hours and then executed during the evening or whenever the computer is idle. Batch processing is particularly useful for operations that require the computer or a peripheral device for an extended period of time. Once a batch job begins, it continues until it is done or until an error occurs. Note that batch processing implies that there is no interaction with the user while the program is being executed.

The opposite of batch processing is transaction processing or interactive processing. In interactive processing, the application responds to commands as soon as you enter them.

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distributed system

A collection of (probably heterogeneous) automata whose distribution is transparent to the user so that the system appears as one local machine. This is in contrast to a network, where the user is aware that there are several machines, and their location, storage replication, load balancing and functionality is not transparent. Distributed systems usually use some kind of client-server organisation.

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