A subsystem provided in order to enable a host system to
obtain access to data on magnetic tape. The subsystem consists of one or more
tape transports (see magnetic tape) and a device controller that incorporates a formatter. The device controller has an interface by which it is connected to
the host. Some manufacturers specify their own proprietary interface, but
several use a common interface specification, originally developed by Pertec,
which has informally become recognized as the industry standard formatter
interface.