Disk Drive Capacity: 20.48 million 36-bit words (= 92MB) formatted.
Peak Transfer Rate: 5.6 microseconds/Word
Access time:
Track-to-track: 7 milliseconds
Average: 28 milliseconds
Maximum: 50 milliseconds
Organization:
128 Words/sector
20 Sectors/track
19 Tracks/cylinder
411 Cylinders/pack
Number of heads: 20
Recording surfaces: 19
Max disks/system: 8
Max drives/controller: 4
Date: 1975. The RP04 is equivalent to the IBM 3330 Mod I. Compare with RP06.
This is the RP04 on our own PDP-11/50. As you can see, the disk packs are removeable. The glass door slides open and the disk is extracted using the clear plastic round cover, then coupled with the case bottom for storage. Exposure of disk heads and surfaces to air particles made these disks much less reliable than today's sealed disks. Also the heads were relatively massive, and rapidly seeking heads caused considerable vibration, and sometimes even made the drives "walk" across the floor.
Photo: Ben Beecher.