Cache is a memory chip on the hard disk controller, which has extremely fast access speed. It is a buffer between the internal storage of the hard disk and the external interface. Because the internal data transmission speed of hard disk is different from that of external interface, cache plays a buffering role in it. The size and speed of cache are important factors directly related to the transmission speed of hard disk, which can greatly improve the overall performance of hard disk. When the hard disk accesses fragmentary data, it needs to constantly exchange data between the hard disk and the memory. If there is a large cache, those fragmentary data can be temporarily stored in the cache, which reduces the load of external systems and improves the data transmission speed.