RA81 Disk Drive

RA81
Manufacturer:	DEC
Year Introduced:	June, 1982
Drive Controller(s):	all SDI controllers
Capacity:	456 Mbytes (formatted)
Transfer Rate:	17.4 Mbits/sec
Revolutions per Minute:	3600
1/2 Revolution Time:	8.3 msec
One Track Seek Time:	7 msec
Average Seek Time:	28 msec
Maximum Seek Time:	50 msec
Total Surfaces:	7 data, 1 servo
Number of Heads:	14 data, 1 servo (read-only)
Tracks per Surface:	1258 (per head)
Sectors per Track:	52
Bytes per Sector:	512
Density:	11,400
Recording Method:	3/2 encoding
Start Time:	20 secs (max)
Stop Time:	20 secs (max)
Physical Size:	26cm x 44cm x 67cm
Weight:	148 lbs
Power Consumption:	644 watts (idle)

4 RA81's in two cabinets

The RA81 is a non-removable-media disk drive from DEC, introduced in June, 1982; it is member of the Digital Storage Architecture. It has a head/disk assembly (HDA) with a capacity of 456 Mbytes, and is a physically large drive (14-inch platters, in a heavy enclosure (10.5" x 16" x 36"); its nominal heat dissipation 644 watts.

It had two heads per surface; not rotationally opposed (to halve maximum access time), but two on each arm; there thus 2,516 usable tracks on each data surface. It was internally operated by a pair of microprocessors, which used 32-bit burst ECC to invisibly repair simple data errors. An RS232 port was provided for diagnostic purposes.

The RA81 connects to the controller via the Standard Disk Interconnect (SDI) bus. Additional drives can be connected to a controller to increase the data storage capacity. The RA81 can also be connected in a dual-port arrangement permitting time-shared access by two controllers.

The RA81 is a self-contained disk drive with built-in cooling system and DC power supply. An RA81 disk drive subsystem is made up of an SDI disk controller and one or more disk drives.

BSD disktab

#
# UCB RA81: use a-b-h-g or a-b-h-d-e-f
ucbra81|UCBRA81|DEC UCBRA81 Winchester:\
        :ty=winchester:ns#51:nt#14:nc#1248:\
        :dt=MSCP:\
        :pa#15884:oa#0:ba#8192:fa#1024:\
        :pb#33440:ob#15884:bb#4096:fb#512:tb=swap:\
        :pc#891072:oc#0:bc#8192:fc#1024:\
        :pd#15884:od#242606:bd#4096:fd#512:\
        :pe#307200:oe#258490:be#8192:fe#1024:\
        :pf#325382:of#565690:bf#4096:ff#512:\
        :pg#648466:og#242606:bg#4096:fg#1024:\
        :ph#193282:oh#49324:bh#4096:fh#512:

External links

• RA81 - documentation at Bitsavers
  • RA81 Disk Drive User Guide (EK-0RA81-UG-001)
  • RA81 Disk Drive Service Manual (EK-0RA81-SV-001)
  • RA81 Field Maintenance Print Set (MP-01359)
• The RA60, RA80 and RA81 Disk Drives and The Digital Storage Architecture - brochure
• RA81 information - Henk Gooijen's extensive RA81 material
  • RA81 internals - fantastic image of a sectioned RA81 drive