The DEC RP06 Disk Drive


Disk Drive Capacity:     39.6  million 36-bit words (= 178MB) formatted.
Peak Transfer Rate:       5.6  microseconds/Word
Access time:
 Track-to-track:         10    milliseconds
 Average:                30    milliseconds
 Maximum:                55    milliseconds
                        128    Words/sector
                         20    Sectors/track
                         19    Tracks/cylinder
                        815    Cylinders/pack
Number of heads:         20
Recording surfaces:      19
Max disks/system:         8
Max drives/controller:    4
Weight:                 600    Pounds

Date: 1977. The RP06 is equivalent to the IBM 3330 Mod II. Compare with RP04. Like the RP04, the disk packs are removeable. Originally, our DEC-20s had approximately four RP06 drives each, but most of them were eventually upgraded to sealed, higher-capacity RP07 and RA81 models. One of our RP06s was "mountable", meaning that users could store their own disk packs in the machine room and have operators mount them upon request.

Once in the early 1980s, many of our RP06s experienced head crashes in the same week. The read/write head literally crashes into the disk surface, ripping and tearing at the oxide and metal, effectively turning the disk drive into a lathe. The heads and the disk are ruined beyond repair and must be replaced and all data is lost (of course the data was faithfully backed up onto 9-track magnetic tape on a daily basis by the machine-room operators). DEC Field Service was at a loss to explain it; higher and higher level engineers were summoned in the familiar process known as "escalation" and various theories were advanced. Finally our own local tech (Warren) figured it out -- around the edges of the disk-well doors were foam-rubber seals, which had all been manufactured at the same time; they had become brittle and were flaking off, sending chunks of ossified latex into the works. He went to the local hardware store and bought some (non-foam) weather stripping to replace the foam, and poof, no more head crashes.

Dean Rubine adds in December 2014:
Your story about head crashes reminded me about a similar one going around when I was at Bell Labs Murray Hill in the late 70s. The story was a new RP06 was installed but wouldn't work. Higher and higher levels of DEC engineers were called in but couldn't diagnose the problem. Finally, the chief engineer is called in to take a look. He powers up the drive and immediately says, "it's spinning backwards."
I forgot to mention this happened to us too. A new disk drive was delivered with a power plug that didn't fit into any available receptacle, so the FE cut it off and connected one that would fit, but got the connections reversed so the disk spun backwards. Live and learn! –fdc
There was another story about an insufficiently anchored RP06 that walked across the machine room floor.

I'll also remember something about a DEC 9 track tape drive that was turned into a musical instrument — you changed pitch by writing blocks of different sizes.

I got most of these stories because as an intern I shared an office in the machine room with an on-site DEC field service rep who kept wrecking company cars.

For more humor, see the bottom of the RP04 page.

Frank da Cruz / / Columbia University Computing History / May 2001 / Updated December 2014