Changing an old CPU for a `better` one

  Eamonncw 19:30 25 Feb 2004

Old CPU is Cyrix 6 x 86 MX pr200.
66Mhz Bus 2.5x

New CPU is AMD K6-2/500 AFX
2.2v core /3.3v i/o

It`s going into an old motherboard, a P5TX
mainboard probably used by Noah`s wife when she counted the animals onto the Ark.
Who can tell me the jumper settings please.

  Eric10 20:35 25 Feb 2004

The PCChips M571 motherboard was a popular choice for the Cyrix range of CPUs. It had 4 slots for Simms and 2 for Dimms. The information I'm about to give you is for this motherboard only. If you don't have the same jumpers as I mention then don't do anything.

Looking down on the motherboard at the CPU end you should have the headers for the front panel LEDs at the left then a block labelled JP6 with voltages written by the pins. To the right of this is a block labelled JP7 and marked ABC. At the extreme right front corner near the memory should be another block labelled JP5 and marked ABCD. The maximum stable FSB for this motherboard was 75MHz. It was possible to run some later boards at 83.3MHz but they could become unstable.

If we are still on course then the jumpers need to be as follows.
JP6: remove all jumpers to get 2.2v.
JP7: for 5x A=1-2, B=2-3, C=2-3, for 5.5x A=1-2, B=1-2, C=2-3
JP5: for 66MHz A=2-3, B=1-2, C=2-3 D=1-2, for 75MHz A=1-2, B=2-3, C=1-2, D=2-3, for 83.3MHz A=1-2, B=1-2, C=2-3, D=2-3

From this we can see that the maximum theoretical speed you could expect from your K6/2 CPU is 83.3 x 5.5 = 458MHz or more realistically 75 x 5.5 = 412MHz. This will still be a great improvement over the Cyrix chip.

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