<computer, parallel> (Or "multi-tasking", "multiprogramming", "concurrent processing", "concurrency", "process scheduling") A technique used in an operating system for sharing a single processor between several independent jobs. The first multitasking operating systems were designed in the early 1960s. Under "cooperative multitasking" the running task decides when to give up the CPU and under "pre-emptive multitasking" (probably more common) a system process called the "scheduler" suspends the currently running task after it has run for a fixed period known as a "time-slice". In both cases the scheduler is responsible for selecting the next task to run and (re)starting it. The running task may relinquish control voluntarily even in a pre-emptive system if it is waiting for some external event. In either system a task may be suspended prematurely if a hardware interrupt occurs, especially if a higher priority task was waiting for this event and has therefore become runnable. The scheduling algorithm used by the scheduler determines which task will run next. Some common examples are round-robin scheduling, priority scheduling, {shortest job first} and guaranteed scheduling. Multitasking introduces overheads because the processor spends some time in choosing the next job to run and in saving and restoring tasks' state, but it reduces the worst-case time from job submission to completion compared with a simple batch system where each job must finish before the next one starts. Multitasking also means that while one task is waiting for some external event, the CPU to do useful work on other tasks. A multitasking operating system should provide some degree of protection of one task from another to prevent tasks from interacting in unexpected ways such as accidentally modifying the contents of each other's memory areas. The jobs in a multitasking system may belong to one or many users. This is distinct from parallel processing where one user runs several tasks on several processors. Time-sharing is almost synonymous but implies that there is more than one user. Multithreading is a kind of multitasking with low overheads and no protection of tasks from each other, all threads share the same memory. (1998-04-24)

Human multitasking is the concept that one can split their attention on more than one task or activity at the same time, such as speaking on the phone while driving a car. Multitasking can result in time wasted due to human context switching and becoming prone to errors due to insufficient attention.

multitasking

multitasking

Media multitasking is the concurrent use of multiple digital media streams. Media multitasking has been associated with depressive symptoms and social anxiety by a single study involving 318 participants.

<operating system, parallel> A type of multitasking where the scheduler can interrupt and suspend ("swap out") the currently running task in order to start or continue running ("swap in") another task. The tasks under pre-emptive multitasking can be written as though they were the only task and the scheduler decides when to swap them. The scheduler must ensure that when swapping tasks, sufficient state is saved and restored that tasks do not interfere. The length of time for which a process runs is known as its "time slice" and may depend on the task's priority or its use of resources such as memory and I/O. OS/2, Unix and the Amiga use pre-emptive multitasking. This contrasts with cooperative multitasking where each task must include calls to allow it to be descheduled periodically. (1995-03-20)

<operating system> (Or "time quantum", "quantum") The period of time for which a process is allowed to run uninterrupted in a pre-emptive multitasking operating system. The scheduler is run once every time slice to choose the next process to run. If the time slice is too short then the scheduler will consume too much processing time but if it is too long then processes may not be able to respond to external events quickly enough. (1998-11-06)

In computing, preemption is the act of temporarily interrupting an executing task, with the intention of resuming it at a later time. This interrupt is done by an external scheduler with no assistance or cooperation from the task.

<parallel, operating system> A form of multitasking where it is the responsibility of the currently running task to give up the processor to allow other tasks to run. This contrasts with pre-emptive multitasking where the task scheduler periodically suspends the running task and restarts another. Cooperative multitasking requires the programmer to place calls at suitable points in his code to allow his task to be descheduled which is not always easy if there is no obvious top-level main loop or some routines run for a long time. If a task does not allow itself to be descheduled all other tasks on the system will appear to "freeze" and will not respond to user action. The advantage of cooperative multitasking is that the programmer knows where the program will be descheduled and can make sure that this will not cause unwanted interaction with other processes. Under pre-emptive multitasking, the scheduler must ensure that sufficient state for each process is saved and restored that they will not interfere. Thus cooperative multitasking can have lower overheads than pre-emptive multitasking because of the greater control it offers over when a task may be descheduled. Cooperative multitasking is used in RISC OS, {Microsoft Windows} and Macintosh System 7. (1995-03-20)