Disk storages are random access stores for mass data in computing systems. A disk storage includes two major components:
Disk drive with one or more storage disks, and storage controller.
The disk drive comprises the mechanical assembly for operating the storage disk, for accessing storage tracks on storage disks, and some electronic circuitry for interfacing with the controller.
The controller supervises the execution of commands supplied to the controller from the processor of the computing system, and performs certain signal processing operations. Signal processing includes conversion of information signals supplied by a data source in the computing system to suitable signals for controlling the drive or for recording on a storage track, and converting signals received from the drive to information signals suitable for communication with the computing system. Controllers differ mainly in the complexity of the signal processing.
Disk drives are characterized by storage capacity, data access time, data transfer rate, and removability of the storage medium. Storage capacity is a function of storage surface and recording density; data transfer rate is a function of rotational speed of the storage medium and recording density; data access time is a function of storage track density and movability of the access mechanism.
Storage removability provides a freedom to let the computing system operate on a large number of different types of data without the need for a large number of disk drives. The exchangeability of storage disks and storage disk packs requires compatibility between disk drives and compatibility between storage disks.
Compatibility between components demands tight control during manufacturing of the components and conservative selection of dimensions and characteristics such as recording density and track density.