What is an Operating System?

The operating system has three major functions: It coordinates and manipulates computer hardware, such as computer memory, printers, disks, keyboard, mouse, and monitor; it organizes files on a variety of storage media, such as floppy disk, hard drive, compact disc, digital video disc, and tape; and it manages hardware errors and the loss of data.

Fig: Operating System

Operating systems are either single-tasking or multitasking. The more primitive single-tasking operating systems can run only one process at a time. For instance, when the computer is printing a document, it cannot start another process or respond to new commands until the printing is completed.

All modern operating systems are multitasking and can run several processes simultaneously. In most computers, however, there is only one central processing unit (CPU; the computational and control unit of the computer), so a multitasking OS creates the illusion of several processes running simultaneously on the CPU. The most common mechanism used to create this illusion is time-slice multitasking, whereby each process is run individually for a fixed period of time.


The below diagram gives a graphical depiction of the interfaces between the operating system and the computer component.

Fig: Operating Systems Interfaces

(Courtesy: www.contrib.andrew.cmu.edu, www.comptechdoc.org)