Magnetic tape system with command prefetch means

Details Magnetic tape system with command prefetch means Magnetic tape system with command prefetch means

1986-07-09

1988-07-12

Canney, Vincent P.

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

360 39, G11B 1518, G11S 509

Patent

active

047573961

ABSTRACT:
A magnetic tape system for efficient and proper prefetching at the end of the tape. The system includes a drive mechanism (1), a drive control unit (2, 20, 21) for controlling the drive mechanism based on commands to write data on the read data from the magnetic tape and a prefetch control unit. The prefetch control unit stores a plurality of write commands from a host system, including write commands which are not accompanied with write data from the host system, and a plurality of read and write data. The drive control unit operates the drive mechanism based on the write commands stored in the first memory. The prefetch control unit reduces the number of prefetched write commands stored therein after receipt of an early warning for the end of tape (EWA) signal. Preferably, the prefetchings of write commands are reduced when a write command sent from the host system is received. The final limit on prefetched write commands is determined by the recording density and the maximum block length of the write commands. The running distance of the magnetic tape may be calculated and prefetch control performed until the calculated value reaches a value corresponding to a second EWA position before the end of the magnetic tape. When the second EWA position is reached, an EOT signal is issued to the host system and prefetched write commands are no longer accepted.

REFERENCES:
patent: 4536806 (1985-08-01), Louth
patent: 4633333 (1986-12-01), Blanco et al.

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