see > Pentium-Pro Processor Card Jumper J9
On server 8639-325, models PT0, PTW, PB0, RB0 Jumper J12 must be placed
to pins 1-2 (PCI/ISA systemboard).
If a PCI/ISA system board is installed (8639-325 models EJ0, ES0, RS0, ESV) then J12 should be placed on pins 2-3.