【Hitachi】 H-8589-1 Magnetic Disk Drive

The H-8589-1 disk drive was developed as a large capacity magnetic disk unit for Hitachi mainframes.
This unit achieved higher speed and precision in head positioning by employing a voice coil motor for the positioning drive mechanism and a servo control system for head positioning control, and using a closed loop control system from the previous open control system. Although these systems have undergone some changes in form over the years, they became the basic systems in today's disk units, and were revolutionary at the time. Surface recording density was 4 times that of previous machines, thereby enabling a capacity of 100Mbyte per replaceable disk pack, and these were positioned as core disks for various types of computer systems.
The recording media was a 14-inch coated disk, and the modified FM (MFM) system was used as the recording system to increase the amount of recorded information with respect to the recording magnetization reversal interval. Use of servo surface information made it possible to detect the rotation position, and thus I/O performance as a subsystem was improved through isolation once from the host unit during the rotational delay. Each DKU has two spindles, and four DKUs were linked and connected to a single disk controller to create a subsystem capacity of 800Mbyte per house.
This unit had media compatibility with the IBM3330-1 disk unit, and disk packs could be exchanged between the two.