在现代计算机系统中，存储器是信息外理的来源与归宿，占据重要位置。

但是，在现有技术条件下，任何一种存储装置，都无法同时从速度与容量两方面，满足用户的需求。

实际上它们组成了一个速度由快到慢，容量由小到大的存储装置层次。-In modern computer systems, memory is the information source and destination outside the grounds, occupying an important position. However, under current technology, any kind of storage device, can not simultaneously both from the speed and capacity to meet the needs of users. In fact they formed a speed from fast to slow, small to large capacity storage device level.