Hard disk is one of the main storage media of computer, which consists of one or more disks made of aluminum or glass, and the disks are covered with ferromagnetic materials. Capacity is the most important parameter of hard disk. Hard disks are divided into solid state drives (SSD) and? Mechanical hard disk (HDD? ), hybrid hard disk (HHD). Solid-state drives use flash particles for storage. Hard drive? Disk is used for storage, and hybrid hard disk is a kind of hard disk that integrates magnetic hard disk and flash memory. Most hard disks are fixed hard disks, which are permanently sealed and fixed in hard disk drives. As the data storage of computer system, the capacity of hard disk is the most important parameter. Generally speaking, the larger the hard disk capacity, the cheaper the price per byte, except for hard disks that exceed the mainstream capacity. Cache (cache? Memory) Yes? Is there a block on the hard disk controller? Memory chip, with extremely fast access speed, is the buffer between internal storage and external interface of hard disk. Because the internal data transmission speed of hard disk is different from that of external interface, cache plays a buffering role in it. ?