【Hitachi】 DK312C Magnetic Disk Unit

To achieve high-density recording with a 3.5-inch disk, this unit used a sputtered disk and metal-in-gap head. An embedded sector servo system was used for the first time for the head positioning servo, and precision was dramatically increased compared to the previous servo system using a servo surface. With the embedded sector servo system, a servo signal is recorded on part of the data track, and head positioning is performed with digital servo control technology using the discrete position information detected there. This system was used as the head positioning technology in all HDDs thereafter for more than 15 years, and is still used today. As the degree of technical difficulty was high, this unit was highly acclaimed as epoch-making.
Also, this unit was for OEM, and it used the SCSi system which was the mainstream interface for 3.5-inch HDDs.

DK312C Magnetic Disk Unit Specifications
Completion date 1989
Memory capacity per spindle 250Mbyte
Surface recording density 40Mbit/square inch
Disk size/quantity 3.5-inch/6 disks
Head type/number per actuator Lightweight MIG/12
Average access time Read:16ms Write:20ms
Disk rotation speed 3,600rpm
Data transfer speed 1.77Mbyte/s

DK312C Magnetic Disk Unit