The context is represented in the PCB of the process. It includes the value of the CPU registers, the process state (see Figure 3.2), and memory-management information. 上下文是保存在PCB里面的。 它包括了CPU寄存器的值， 进程状态， 和内存管理信息。 Generically, we perform a state save of the current state of the CPU, be it in kernel or user mode, and then a state restore to resume operations. 通常我们保存CPU的当前状态，记录是在内核（kernel）模式还是在用户模式，然后记录恢复当前操作的状态。
Switching the CPU to another process requires performing a state save of the current process and a state restore of a different process. 切换CPU从一个进程到另外一个进程要求保存当前进程状态和恢复另外一个进程状态。 This task is known as a context switch. 这任务叫做上下文切换。 Context-switch times are highly dependent on hardware support. 上下文切换的时间是很依赖硬件的。 How the address space is preserved, and what amount of work is needed to preserve it, depend on the memory-management method of the operating system. 内存空间如何保存和要保存的工作量是依赖于操作系统内存管理策略的。