【NEC】 D5655 Hard Disk Unit

In May 1988, NEC announced the D5655 5-inch, high-capacity, high-speed hard disk unit for OEM.

This unit improved performance of the magnetic recording media, increased recording density by using 2-7RLL (Run Length Limited) code, which has a minimum magnetization reversal 1.5 times that of MFM (Modified Frequency Modulation), and achieved a memory capacity of 179.8MB, the highest in Japan for a 5.25-inch thin hard disk unit.
An average seek time of 18msec, the fastest in Japan, was achieved by, among other things, lightening the magnetic head movement mechanism and using a high-performance voice coil motor.
Noise during random seek was a low 45 decibels or less.

D5655 Magnetic Disk Specifications
Disk diameter(inch) 5.25
Number of disks 4
Number of heads 7
Number of cylinders 1224
Recording density(bpi) 19610
Track density(tpi) 1240
Recording system 2-7RLL
Memory capacity (unformatted) (MB) 179.8
Average seek time(msec) 18
Average rotational delay(msec) 8.4
Data transfer speed(kB/sec) 1250
Rotation speed(rpm) 3573
Unit dimensions(mm) 146(W)×203(D)×41(H)
Date first shipped April 1988

D5655 Magnetic Disk