The multiprocessor bus-to-PCI bridge is a special adapter that physically plugs into two sockets, one on the multiprocessor bus and one on the PCI bus. The circuitry on this card controls the movement of data between the processor complexes, memory cards and the I/O adapters on the Micro Channel and PCI buses. It implements a split bus design so that during slower I/O operations the multiprocessor bus can be made available for processor to memory transfers without having to wait on the I/O transfer.

PCI Bridge Card  FRU 75H9141 IPB Bridge card 
                                - use 33Mhz PCI bus clocking Date of 95

JP1 is a three pin header. 1-2 is Primary bridge. 2-3 is Secondary bridge. 
JP2 is a two pin header 

PCI Bridge Card FRU 76H7134 Date of 94

JJ1 Primary 1-2 (bottom) Secondary 2-3 (top)
 

SUBJECT: INTERMITTENT HANGS - SERVER PC720(8642) 

SYMPTOM: 
Intermittent hangs / traps on Server 720 / 8642 

PROBLEM ISOLATION AIDS: 
Check settings of jumper J24 on system and manufacturing part number of PCI bridge card 

FIX: 
Bridge card 07H1107 (fru Part Number 71G0694) requires J24 on the system board to be open circuit 

Bridge card 75H7667 (fru Part Number 71G0694) requires J24 pins 1+2 to be Short circuit ( ie. the 2 pins of J24 nearest the back of the machine.) 

REASON : 
J24 pins 1+2 S/C sets the PCI bus speed to 33MHz. ( new Bridge card ) 
J24 pins o/c sets the PCI bus speed to 25MHz. ( old Bridge card )