Principle of operation

Says Ordonnanceur Operating system of a Ordinateur. The Ordonnanceur distributes the time of the Processeur between different the process. In a préemptif system (contrary to a collaboratif system) the ordonnancor can constantly stop a task in the course of execution to allow another task to be carried out.

In a Multi-task operating system , a task can be specified like préemptive or nonpréemptive . In the first case, a task can be put at the state “ready” with the profit of a task of more raised priority or of an interruption. In the second case, a task can be suspended only on the profit of an interruption.

Some examples

Concretely, a préemptif operating system permanently preserves the upper hand on the tasks carried out by the processor, contrary to an operating system nonpréemptif, or collaboratif, in which it is the process in the course of execution which takes the hand and is only judge of the moment when it returns it. The most obvious advantage of a préemptif system is that it can permanently decide to stop a process, mainly if this one fails and causes the instability of the system.

As example, one can quote among the operating systems collaboratifs: all operating systems of Microsoft until Windows 98 (including Windows 3.1 and Windows 95); among the operating systems préemptifs count: all operating systems starting from Windows 2000 (of which Windows XP and Windows Vista), the systems Unix, such as Mac OS X and Linux, the system AmigaOS.

Attention, it is not a question of collaboratif but of co-operative… Starting from Windows 95, the Windows systems adopt the Win32 core and appear préemptifs even if the effectiveness of such multitasks is discussed within the community (at least for versions 95,98 and Me).

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