RA81 Disk Drive
From Computer History Wiki
The RA81 is a DEC disk drive, introduced in 1982. It is a moving head (SDI Winchester) fixed disk drive. It has a non-removable media using a head/disk assembly (HDA) with a capacity of 456 Mbytes.
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.
Specifications
Key figures are the following:
- Storage capacity of 456 Mbyte in 16-bit word format
- 1258 cylinders
- 17.4 Megabit/sec peak transfer rate
- 28 mSec. average positioning rate (average seek time)
- 7 mSec. maximum positioning rate (cylinder to cylinder)
- 50 mSec. maximum seek (innermost to outermost cylinder)
- 8.3 mSec. average rotational latency
- 3600 RPM rotational speed
- Heat dissipation 644 Watt nominal
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)
- RA81 information - Henk Gooijen's extensive RA81 material
- RA81 internals - fantastic image of a sectioned RA81 drive
- The RA60, RA80 and RA81 Disk Drives - combined RA60/RA80/RA81 sales brochure
