Tape memory with integral disk index on reel

Abstract

A peripheral memory controller controls a helical scan magnetic tape recorder so as to record and play back data files in parallel tracks on a magnetic tape. The tape is contained in a cassette having a magnetic disk fixably mounted on one reel of the cassette so that the movement of the tape and rotation of the disk are simultaneous. The peripheral memory controller refers to a file allocation table stored in one (or more) tracks on the disk, in order to correlate data file descriptions with track locations on the tape. A disk head rapidly scans the file allocation table disk track(s) within just one (or a few) revolutions of the disk while transmitting the contents of the table to the peripheral memory controller. The controller deduces therefrom the tape track location of a particular data file and commands the tape to be transported to that location in order to access that file. In another embodiment, sub-file allocation tables, each describing the tape track location of each sub-file within a given data file, are recorded in other disk tracks whose locations are recorded, in turn, in the file allocation table disk track. In order to take advantage of the co-movement of the tape and the disk, each sub-file allocation table stores the names of sub-files whose tape track locations fall within a length of tape covered during one rotation of the reel and disk, so that each sub-file allocation table disk track may be scanned completely while maintaining the position of the tape within the tape location range of the corresponding sub-file allocation table.