It is common for modern processors to be running multiple processes at one time. Each process has an address space associated with it. To create a whole complete address space for each process would be much too expensive, considering that processes may be created and killed often, and also considering that many processes use only a tiny bit of their possible address space. Last but not least, even with modern improvements in hardware technology, machine resources are still finite. Thus, it is necessary to share a smaller amount of physical memory among many processes, with each process being given the appearance of having its own exclusive address space.

The most common way of doing this is a technique called virtual memory, which has been known since the 1960s but has become common on computer systems since the late 1980s. The virtual memory scheme divides physical memory...