The CPU current-register-set pointer is changed to point to the set containing the
new context, which takes very little time. If the context is in memory, one of the contexts
in a register set must be chosen and be moved to memory, and the new context must be
loaded from memory into the set. This process takes a little more time than on systems
with one set of registers, depending on how a replacement victim is selected.
參考答案:cpu当前寄存器。。。
去找中文的书看吧，楼上太不负责了...