The middle digit of the sub-model identification indicates type and clock speed
of the installed CPU, except for the early PS/2 systems
(all models 25, 30, 50, 50Z, 60, 70, P70, P75, and 80) where it has a different meaning.
List compiled by David Beem.
We are making a few assumptions here (marked as "Theory"), to see if it can be fully pinned down...
|3||386SX-16 (duplicate of '1'), Theory: working FLOAT pin?|
|6||486SLC2-40 (CPU daughtercard on 8556/8557)|
|7||Theory: 486SLC3-60? (CPU daughtercard on 8556/8557)|
|B||486SLC2-50 (9533/9553/9556/9557 planar or CPU daughtercard on 9556/9557)|
|E||486SLC3-75 (9556/9557 planar or CPU daughtercard on 9556/9557)|
|U, X||486SX-33 (Theory: one PGA, the other PQFP?)|
Possible missing encodings: POD63/POD83, IBM 486DLC2, 486SL.
IBM even had little stickers included with the CPU daughtercards to put over the sub-model label.
What about zero?
What about 0 for the Type 0 and 0- 386DX-20 complexes in the Model 90s?
The 8590-402 was a '4' "Special Bid" unit that makes use of the sub-model
middle digit CPU encoding for other uses - There is no '0' CPU as far as I know.
Another late night thought is the Intel 486DX3-75 and classic Pentium 100MHz
CPUs not on any factory PS/2 configuration. I believe IBM attempted to cover
every Intel and IBM CPU from the 386SX to classic Pentium at all offered clock
speeds. IBM was anal enough to have a separate encoding of whether the same IBM
486SLC2 CPU daughtercard was running at 40MHz (from an 8556/8557 planar host)
or 50Mhz (from a 9556/9557 planar host or 9533/9553 planar) internally.
I also thought about checking the CPU encoding for the PS/2 N45 ("PS/2 Note")
sub-models since it uses the Intel 486SL-25 CPU (there is also an Intel 486SL-33)...