H-8564 Magnetic Disk Drive

The H-8564 disk drive was the first product that Hitachi developed by itself as a magnetic disk unit for its HITAC 8000 Series of mainframes. It was the base for Hitachi’s business of magnetic disks.

Memory capacity was 7.25 M byte per unit, average access time was 75 ms, and data transfer speed was 156 K byte/s. A disk pack structure with six 14-inch coated disks was used as the recording media. The top and bottom disks were only used on one side, and the system was equipped with 10 magnetic heads.

To detect the disk rotation position, notches were provided in an aluminum disk added at the bottom. Detection was done with a magnetic transducer, and the system detected things like the index indicating the start of a track or a sector. For actuator drive, positioning with open control was done using a hydraulic mechanism.

An FM system employing double-frequency was used for recording modulation. Clock bits and data bits were arranged alternately, and discrimination between "1" and "0" was done by checking for the presence of magnetization reversal at the data bit position. This unit had media compatibility with the IBM 2311 disk unit, and disk packs could be exchanged between the two.