【Hitachi】 H-8564 Magnetic Disk Drive

The H-8564 disk drive was the first product developed by Hitachi as a magnetic disk unit for the Hitachi HITAC 8000 Series of mainframes. 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.

H-8564 Magnetic Disk Drive Unit Specifications
Completion date June 1967
Memory capacity per unit 7.25Mbyte
Memory capacity per spindle 7.25Mbyte
BPI 1,100BPI
Surface recording density 0.11Mbit/square inch
Disk size/quantity 14-inch/6 disks
Head type/number per actuator Heavyweight inductive/10
Average access time 75ms
Disk rotation speed 2,400rpm
Data transfer speed 156Kbyte/s

H-8564 Magnetic Disk Drive