Operating Systems: Concurrent and Distributed Software Design

4.2. Processes and processors

There are often far fewer processors than the processes we should like to use in a system. If this was not the case we could dedicate a processor permanently to each process. When the process has something to do, it executes on its processor; when it has nothing to do its processor idles. In practice, the operating system must perform the function of sharing the real processors among the processes. We shall see that this function can be regarded as creating virtual processors, one for each process; that is, the operating system is simulating one processor per process.

In Section 3.2.5 we saw that interrupts from devices may be given a priority ordering and that the handling of a low-priority interrupt is temporarily ...