1. How can the operating system provide the illusion of a nearly-endless supply of said CPUs?
The OS creates this illusion by virtualizing the CPU. The basic technique, known as the time-
sharing the CPU, allows users to run as many concurrent processes as they would like. Potential
cost is performance, as each will run slowly if the CPU(s) must be shared. To implement virtualization
of the CPU, and to implement it well, the OS will need both some low-level machinery mechanisms;
mechanisms are low-level methods or protocals that implement a needed piece of functionality.
Operating System: Three Easy Pieces --- Process (Note)
原文：http://www.cnblogs.com/miaoyong/p/4850821.html