HP A2051-69007 - 64MHz system processor board - 64MHz System Processor Board - Plugs into Slot to the Right of the Multifunction I/O Board Retail
HP A2051-69108 - 96MHz system processor board - 96MHz System Processor Board - Plugs into Slot to the Right of the Multifunction I/O Board Retail
HP A6961-67105 - Midplane riser board - Has slots for the processor board, memory board, and I/O base board Retail
HP A3641-69005 - 4 slot HP-HSC expansion board - Does not include the HP-HSC expansion I/O board tray Retail