This is an example of a memory hierarchy, where you have a little bit of fast memory, which is expensive, slightly more medium-speed memory, which is less expensive, and then a lot of slowish memory, which is cheap.

这是内存层次结构的一个例子，其中有一点快速内存， 价格昂贵，中速内存稍多一点， 价格便宜，然后是很多速度较慢的内存， 价格便宜。