SNIP

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>For example, from:
>http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/multitasking.asp
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>A multitasking operating system divides the available processor time among the processes or threads that need it. The system is designed for preemptive multitasking; it allocates a processor time slice to each thread it executes. The currently executing thread is suspended when its time slice elapses, allowing another thread to run. When the system switches from one thread to another, it saves the context of the preempted thread and restores the saved context of the next thread in the queue.
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>The length of the time slice depends on the operating system and the processor. Because each time slice is small (approximately 20 milliseconds), multiple threads appear to be executing at the same time.
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SNIP
Hi Nick,

I just want to reinforce, for other readers, that this describes how MS implements "multitasking" in Windows and that there can well be more to the feature than simple time slicing (as was so in OS/2, for instance).
Specifically, 'interrputs' can also 'drive' multitasking. Interrupts like:
- a process issues a WAIT, causing another (ready) task to gain control;
- a process does an I/O operation resulting in an implied WAIT that the OS can exploit to give control to another ready task;
- an I/O for a higher priority task completes while some other task is running, resulting in suspension of the running task and ransfer of control to the tasking issuing the (now completed) I/O.
- a few others...

cheers