Multitasking is the use of a single processor, or set of processors, to run more than one task at a time. Multitasking usually is seen on minicomputers which must integrate the demands of multiple users. However, it is being incorporated more frequently into the design of personal computer operating systems. The ability to multitask allows processors to make optimum use of their speed when dealing with more than one process.
Three different types of multitasking are commonly used. They are context switching, cooperative multitasking, and time-slice multitasking. Each method is distinct and finds use in different computer environments. Context switching is the simplest type of multitasking. In Context switching, more than one application is loaded and operable, but processing time is given only to the one, which is presently in use (said to be "in the foreground"). The user can switch to the other (background) application to allow it to have processing time, but the two applications cannot be processed simultaneously. Even with this limitation, the format of context switching significantly enhances processing time of multiple applications.
Another common type of multitasking is called cooperative multitasking. An improvement over context switching, cooperative multitasking allows idle processor time of the foreground application to be given to the background application. Enough idle time is usually in the foreground application (such as while waiting for the user to respond with keyboard input) that cooperative multitasking usually can multitask with greater efficiency than simple context switching. Recently, more personal computers are being developed to support this kind of multitasking.
A third, less common, type of multitasking is called time-slice multitasking. Commonly used in minicomputer workstations, such as those supported by OS/2, the microprocessor time is divided among the many tasks of multiple users. The time division may be based upon sequential order, as the task was given to the microprocessor, or may be determined by an assigned priority level. This type of multitasking more closely resembles simultaneous processing, due to the speed of the microprocessors used.
