Multitask

Multitasking is the feature of modern operating systems that allows multiple processes or applications to run seemingly at the same time, sharing one or more processors.

Multitasking operating systems are capable of servicing more than one process at a time to allow many more programs to run.

This category also includes all systems that simultaneously meet the needs of two or more users—called multi-user systems—that share the same resources. This type of system is used especially in networks. In short, it is about splitting time.

Types of multitasking

Cooperative

In cooperative multitasking the operating system gives control to a process and it is this process that gives up control again when it voluntarily decides that it cannot continue its execution, becoming on standby. Being dependent on the running process itself can be problematic, since if the user process is interrupted and does not give up the CPU to the operating system, the entire system will be blocked, that is, without being able to do anything. It also gives rise to very irregular latencies and the impossibility of taking this scheme into account in real-time operating systems. Microsoft Windows versions 3 through 95 (all running under MS.DOS) are an example of this type of cooperative multitasking Operating System. It was also used by Apple in Mac OS Classic.

Appropriative or preventive

In preemptive multitasking or preemptive multitasking, the operating system is in charge of managing the processor(s), dividing the usage time among the processes that are waiting to use it. Each process uses the processor for short periods of time, but the end result is virtually the same as running all at the same time. Examples of systems of this type would be Unix and its derivatives (FreeBSD, Linux), VMS and derivatives, AmigaOS, Windows NT, IBM360 or DEC PDPs. The Sinclair QL's operating system used this type of multitasking.

Real

Only occurs on multiprocessor systems; several processes are actually running at the same time on different microprocessors; It is also usually preferred. Examples of operating systems with that capability: Unix variants, Windows NT, Mac OS X.