【Hitachi】 H-8575 Magnetic Drum Unit

Magnetic drums were widely used due to features such as a short average access time and a low error rate in recorded data. H-8575 was commercialized in 1975 as a magnetic drum unit for the HITAC M Series, with the aim of further shortening average access time and greatly improving capacity.

Average access time was halved to 5.3ms by doubling drum rotation speed from the previous 3,000rpm to 6,000rpm. Capacity was roughly quadrupled to 15MB (megabyte). This was achieved by taking measures to increase density, such as halving spacing between the floating head and media to approximately 1μm, and by increasing track density. Data transfer speed was also a high 12Mbit/s, and at the time, this magnetic drum had the best performance in the world.

This magnetic drum was a product developed through joint research by Nippon Telegraph and Telephone Public Corporation and Hitachi, Ltd., and it was also used in the data communication systems of Nippon Telegraph and Telephone Public Corporation.

H-8575 Magnetic Drum Unit Specifications
Unit model name H-8575
Completion date 1975
Head type Floating head
Head floating distance 1.0 μm
Memory capacity 15 MB
Recording system NRZ-I recording system(8/9bit conversion)
Average access time 5.3 ms
Data transfer speed 12Mbit/s
Drum Name of unit used FV-2540F
Number of tracks 1,024
Rotation speed 6,000 rpm
Rotor dimensions 250 ø×420 mm
Recording density 156 bit/mm
Connected systems Digital switching systems/DIPS/
Subscriber data communication systems
Seat reservation systems
HITAC-M Series

H-8575 Magnetic Drum Unit, AppearanceH-8575 Magnetic Drum Unit, Internal Mechanism