RA80 Disk Drive

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Manufacturer: DEC
Drive Controller(s): all SDI controllers
Capacity: 121 Mbytes
Transfer Rate: 1.2 Mbytes/sec
Average Access Time: 33 msec
Revolutions per Minute: 3600
1/2 Revolution Time: 8.3 msec
One Track Seek Time: 6 msec
Average Seek Time: 25 msec
Maximum Seek Time: 50 msec
Total Surfaces: 7 data, 1 servo
Number of Heads: 14 data,
1 servo (read-only)
Tracks per Surface: 561 per head (total)
546 (usable for data)
Sectors per Track: 31
Bytes per Sector: 512
Tracks per Inch: 478
Density: 6339 (max; inner track)
Recording Method: MFM
Start Time: 15 secs (avg);
40 secs (max)
Physical Size: 26cm x 44cm x 67cm
Weight: 147 lbs (approx)
Power Consumption: 720 watts


The RA80 Disk Drive is a Standard Disk Interconnect non-removable-media disk drive from DEC. A physically large drive (14-inch platters, in a heavy enclosure 10.5" x 16" x 36"), its capacity was 121 Mbytes.

It had two heads per surface; not rotationally opposed (to halve maximum access time), but two on each arm; there thus 1,092 usable tracks on each surface. It was internally operated by a microprocessor which used 32-bit burst ECC to invisibly repair simple data errors.

It was apparently the SDI version of the R80 Disk Drive. The RA80 can also be connected in a dual-port arrangement, permitting its use by two controllers.

4.3 BSD disktab

a80|RA80|DEC RA80 Winchester:\

External links