The Rough Guide to MBus Modules
Introduction Buses Modules Systems Chips Miscellany


Note: Force Computers produced a wide range of board-level products: single-board computers, special-purpose co-processor boards, and so on; mainly VME/SPARC-based, but also a few MultiBus and ISA/x86 boards and, IIRC, an SBus Transputer co-processor board. The SBC products were used in many third-party special-purpose, embedded and custom systems.

With the demise of Force Computers, the VME/SPARC designs were taken over by Themis.


The VME SPARC-20 is a "single-board computer" for VMEbus enclosures.

The VME SPARC-20 has a single 40/50MHz MBus slot, 2 SBus slots, externally-accessible AUI, 10BaseT, MII, Sun-keyboard and 50-pin Fast SCSI-2 sockets, and an external reset switch.

The board-level bus architecture is probably the same as the SPARCserver-600 system-board, but with a SPARCstation-20 memory-controller (EMC rather than SMC).

As can be seen from the pictures, there is a second MBus-style "5-ground-blade" connector on the board, but it seems so far away from the first that surely it cannot be for a second CPU module?

Instances of systems built around a VME SPARC-20 have been seen fitted with SM41, SM50, SM51, SM61, HM100S-256, HM125S-256, HM133S-256, and HM150S-512 modules. Many other MBus modules are likely to work, with the exception of modules using CY7C601, CY7C602, HMx1S-256, all RT620D CPUs, and all SuperSPARC modules clocked below 40 MHz, and just possibly SuperSPARC-II CPUs as well.

Judging from the pictures, double-width modules will fit, although it is unknown whether the PROM firmware can handle two CPUs or not.

The overheating risks for the VME SPARC-20 are heavily dependant on the (typically custom) VME chassis it is deployed in. Thus exact advice cannot be given here.

Some of the systems built around the VME SPARC-20 run stock Solaris 2.4, 2.5 and 2.5.1. Solaris releases after 2.5.1 do not support VMEbus peripherals or VMEbus memory, so would restrict you to only the devices onboard the VME SPARC-20 itself, plus any directly attached SBus cards.

Introduction Buses Modules Systems Chips Miscellany
Mike Spooner, revised 24th February 2002