【Hitachi】 H-8576 Magnetic Disk Unit

The H-8576 magnetic disk unit was developed as a device with twice the capacity per unit of the H-8595 (317MB/sp).
This unit achieved both higher reliability and lower cost by improving the small disk system, which was just establishing a track record at this time, to a level capable of handling mission critical applications. For large disks, equipment was previously developed by imitating the system of IBM machines, but this unit tried to reduce connection parts such as connectors by employing rotary actuators and completely sealed HDA which were used at the time for small disks, and electronics were directly mounted to the HDA, just like a small disk.
To reduce costs, two rotary actuators were provided on a single spindle, and the system was equipped with two access mechanisms with independent addresses per HDA. The two actuators each held their own separate disk surface, and compatibility with the IBM3350 was achieved with a capacity of 317MB.
The power supply system used a rough rectification system which employed with directly rectified CVT transformer output as is. This had fewer parts, and markedly better reliability than the previous dropper/switching system.
Although the mechanism was the rotary actuator type, this was the first large actuator holding six 14-inch disks, and many problems arose which did not appear with small disks. However, the persons in charge of the Hitachi research center and plant organization, and the engineers in charge of control circuits all worked tightly together to solve the problems, and brought the project to a successful conclusion.

H-8576 Magnetic Disk Unit Specifications
Completion date January 1981
Memory capacity per unit 1,260Mbyte/DKU
Memory capacity per spindle 630Mbyte
BPI 6,250BPI
Surface recording density 4.5Mbit/square inch
Disk size/quantity 14-inch/11disks
Head type/number per actuator Lightweight NiZn ferrite/20+1(servo)
Average access time 18ms
Disk rotation speed 3,600rpm
Data transfer speed 1.2Mbyte/s

H-8576 Magnetic Disk Unit