RM02/03 disk drive

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Manufacturer: Digital Equipment Corporation
Drive Controller(s): RH10 (PDP-10)
RH20 (KL10)
RH70 (PDP-11/70)
RH780 (VAX-11/780)
RH750 (VAX-11/750)
Capacity: 67 Mbytes
Transfer Rate: 2.48 μsec/word (RM02/16-bit)
2.79 μsec/word (RM02/18-bit)
1.65 μsec/word (RM03/16-bit)
1.86 μsec/word (RM03/18-bit)
Average Access Time: 42.5 msec (RM02)
38.3 msec (RM03)
Revolutions per Minute: 2400 (RM02)
3600 (RM03)
1/2 Revolution Time: 25.9 msec (RM02)
17.3 msec (RM03)
One Track Seek Time: 6 msec
Average Seek Time: 30 msec
Maximum Seek Time: 55 msec
Total Surfaces: 6 (5 data, 1 servo)
Tracks per Surface: 823
Sectors per Track: 30 (18-bit words)
32 (16-bit words)
Words per Sector: 256
Recording Method: MFM
Physical Size: 21-5/8?" W x 39" H x 33" L
Weight: 430 pounds

The RM02 and RM03 were MASSBUS large removable-pack disks. They were effectively identical, except that the RM03 rotated faster (3600 RPM, versus 2400 RPM for the RM02). The RM02 provided 806 KB/s transfers; the RM03 was 1200 KB/s transfers.

Both supported both 15-bit and 18-bit words; user data is protected by a 32-bit ECC per sector. RM0x drives are dual-ported, allowing any drive to be attached to two different controllers. Generally a maximum of 8 drives were supported per device controller.

They both used 5-platter RM03P (type 9877) packs; neither side of the top and bottom platters were used, however - they were only there for protection. Of the other 6 surfaces, one was read-only, pre-recorded by the manufacturer with servo information; the drive had the capability of seeking to a 200 μinch offset under command, to allow the attempted recovery of otherwise-unreadable data.


As usual with MASSBUS devices, most device-specific registers are actually in the device; the MASSBUS interface to the host computer only contains generic registers. In the RM02/03, the host's MASSBUS device controller contains a small number of registers (5 in the |RH11), and the drive contains 16. They are:

Name MASSBUS Address Function
RMCS1 Control 00 Function code, GO
RMDA Desired Sector/Track Address 05
RMDS Drive Status 01 Non-error status
RMER1 Error 1 02
RMAS Attention Summary 04 One bit per drive
RMLA Look-Ahead 07 Current sector
RMMR1 Maintenance 1 03
RMDT Drive Type 06
RMSN Serial Number 10 Low 4 digts
RMOF Offset 11 1 bit head offset
RMDC Desired Cylinder 12 For seek
RMHR Holding 13 Unused; zeros
RMMR2 Maintenance 2 14
RMER2 Error 2 15
RMEC1 ECC Position 16
RMEC2 ECC Pattern 17

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