The most important task of an operating system is to process commands and to provide coordination between different processing tasks. Here are details about multitasking, processing commands, multithreading, multiprocessor and miscellaneous tasks of an Operating System (OS).

Processing Commands: The operating system interprets instructions entered through the keyboard. When one uses an application program, the program’s commands are interpreted by the operating system. For example, one might open a document by clicking a button on the program’s toolbar. At another time the user might do so by dragging the file onto the application’s icon and dropping it. The operating system interprets these commands and copies the document on the disk of the computer.

Multitasking: Modern operating systems allow multitasking, that is to perform multitasks, at the same time with different programs. For example, one could download a large file from the Internet with one program, while editing a document with another. Older operating systems could run only one program at a time. Since most systems have only one microprocessor, they allow multiple programs to run by quickly switching back and forth between them. Although only one program is actually active at a time; the processor switches so fast that they all appear to be active. This process is called time-slicing or task-switching because it slices up the CPU’s time as it switches between the running applications. Today’s system use a form of multitasking called preemptive multitasking. In this type of multitasking access to the microprocessor is controlled so that one application cannot seize it and hold it for long a period. One application can “preempt” another application to get a fair share of the processor’s time.

Multithreading: Most applications process data and commands sequentially, i.e. when one task is finished they begin another. The application therefore follows a single thread from the beginning of a session to the end and individual operations are strung like beads on a necklace. A multithreaded operating system on the other hand lets application programs start and run two or more threads simultaneously. It is similar to multitasking within a single program. For example, one thread in a word processing program can be reading the pressed keys while a second thread displays data on the screen and a thread prints the document.

Multi-user Support: Some operating systems are designed so that many users can be connected to the system at the same time. Multi-user operating systems are also multitasking because the multiple users run their programs at the same time.

Multiprocessor Support: Some applications need huge processing power. For example, anyone doing forecasting, modeling, simulating, or computer aided design needs enormous computing power. Some operating systems support multiple processors – in some cases hundreds or even more.

Miscellaneous Tasks: In addition to the processing tasks discussed, an operating system also performs the following tasks:

• The operating system continually monitors the system and if it detects something wrong, it outputs an error message.
• The operating system ménages the use of memory and runs each program in its own protected space to that a problem with one program will not affect others.
• The operating system allocates peripheral devices for different tasks.
• To conserve power, power management cuts power at those times when it is not needed.
• Manages file stored on disks.