Type Size Tracks Sectors Heads SectorSize Encoding Capacity Format
RX01  8     77     26      1      128       FM       256K   IBM 3740
      8     77     26      2      128       FM
RX02  8     77     26      1      256     FM+MFM     512K   DEC RX02
RX03  8     77     26      2      256     FM+MFM    1024K   DEC RX02

      3½    80     10      2      256       FM       400K
      5¼    80     10      2      256       FM       400K

RX24  3½    80      9      2      512       MFM      720K    720K PC
RX23  3½    80     18      2      512       MFM     1.44M   1.44M PC
RX26  3½    80     36      2      512       MFM     2.88M   2.88M PC

RX31  5¼    40      9      2      512       MFM      360K    360K PC
      5¼    40     15      2      512       MFM
      5¼    80      9      2      512       MFM
RX33  5¼    80     15      2      512       MFM      1.2M    1.2M PC/AT


RX50  5¼    80     10      1      512       MFM      400K    RX50
      5¼    80     10      2      512       MFM      800K


            RXx0      RXx1        RXx2        RXx3        RXx4       5 RXx6
RX0x 8"               1x77x26x256 1x77x26x512 2x77x26x256
RX1x 5.25"
RX2x 3.5"                                     2x80x18x512 2x80x9x512 - 2x80x36x512
RX3x 5.25"            2x40x9x512              2x80x15x512
RX4x 8"
RX5x 5.25"  1x80x10x512


RXx- 0 0 0  8"        RX-x 0 0 0  HD:1             80tk   DD
     0 0 1                 0 0 1  HD:1,HD:2   77tk,40tk   SD,DD
     0 1 0  3.5"           0 1 0  HD:1        77tk        DD
     0 1 1  5.25"          0 1 1  HD:3        77tk,80tk   DD
     1 0 0                 1 0 0  HD:4             80tk   DD
     1 0 1  5.25"          1 0 1
     1 1 0                 1 1 0  HD:6             80tk   DD
     1 1 1                 1 1 1
       | |
       0 0  8"
       0 1  5.25"
       1 0  3.5"
       1 1  5.25"



3.5" drive 300rpm


RX01  1side 77trk 26sec 128byte SD           360rpm 8"
RX02  1side 77trk 26sec 256byte mixed SD/DD  360rpm 8"
RX33  2side 80trk 15sec 512byte HD   500kbit/s 360rpm identical to 8" - PC/AT "1.2MB drive"
RX50  1side 80trk 10sec 512byte DD   250kbit/s 300rpm 

RX24 3.5" 720K
RX26 3.5" 1440K



The first 2 letters will tell you the device type (first) and the
technology (second). After that, the numbers are somewhat random.  DEC
started most of the older series with "01" and worked their way up, but
the newer series start at random places and often have gaps. DEC
apparently picked the 50 series to get a previously-unused matching set of
numbers - RX50 for floppy, RD50 for hard drive, TK50 for tape.

As technology evolved, sometimes numbers in the sequence referred to a
slightly different device form factor. For example, the RF3x disks started
out as 5.25" half-height DSSI drives and the RF7x disks were 5.25"
full-height. But later RF3x drives were 3.25" (with adapter brackets to
fit in existing 5.25" mounting).

Tx = tape device

Rx = disk device

xD = ST-506 hard drive
xF = DSSI drive
xH = controller (Massbus)
xK = cartridge drive, initially from OEMs (up to RK05), later built by DEC (RK06/7)
xL = cartridge drive by DEC
xM = pack drive, usually CDC (and successors)
xP = pack drive, usually Memorex (and successors)
xX = floppy
xZ = SCSI