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CPU Type Encoding
What About Zero?
Further Reading
List compiled by David Beem. Sources: PS/2 Assistant, empirical evidence.
CPU Type Encoding
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, 60, 70, P70, P75, and 80) where it has a different meaning.
| Code | Meaning |
|---|
| 1 | 386SX-16 |
| 2 | 386SLC-16 |
| 3 | 386SX-16 (duplicate of '1'), Theory: working FLOAT pin? |
| 4 | 386SX-20 |
| 5 | 386SLC-20 |
| 6 | 486SLC2-40 (CPU daughtercard on 8556/8557) |
| 7 | Theory: 486SLC3-60? (CPU daughtercard on 8556/8557) |
| 8 | 386DX-20 |
| B | 486SLC2-50 (9533/9553/9556/9557 planar or CPU daughtercard on 9556/9557) |
| C | 386DX-25 |
| D | 386DX-33 |
| E | 486SLC3-75 (9556/9557 planar or CPU daughtercard on 9556/9557) |
| F | Theory: 486SX-16? |
| G | 486SX-20 |
| H | 486SX-25 |
| I | Theory: 486DX-16? |
| J | 486DX-25 |
| K | 486DX-33 |
| L | 486DX2-50 |
| M | 486DX-50 |
| N | 486DX2-66 |
| P | Pentium 60 |
| Q | Pentium 66 |
| T | 486DX4-100 |
| U, X | 486SX-33 (Theory: one PGA, the other PQFP?) |
| Y | Pentium 90 |
Note: We are making a few assumptions here (marked
as "Theory"), to see if it can be fully pinned down...
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?
From Tim:
What about 0 for the Type 0 and 0- 386DX-20 complexes in the Model
90s?
David replies:
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 100
MHz 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 40 MHz (from an 8556/8557
planar host) or 50 MHz (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)...
Further Reading
IBM PS/2 Assistant - Understanding PS/2 Model Numbers
"Numerological" - CSIPH Thread
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