RM02/03 disk drive
| RM02/RM03 | |
| Manufacturer: | Digital Equipment Corporation |
|---|---|
| Drive Controller(s): | RH10 (PDP-10) RH20 (KL10) RH11 (UNIBUS) 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.
Registers
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 |
