From Archimedes to Risc PC

How Acorn managed to test the Risc PC without building a whole one

The release of the RISC OS source code by ROOL has unearthed a mass of interesting historical data. Here is a short discussion of one find, the prototype systems used to test some Risc PC components without using the whole Risc PC architecture.

ROOL source link

These machine definition files suggest versions of RISC OS were built for these systems rather than them being OS-less test systems.

The two new chips, an ARM6 and the VIDC20 video controller, could be tested without having to rewrite the OS to handle the other architecture changes, the new MMU and IOMD IO controller.

Machine CPU MMU Video IO Controller IO Support
Pre-existing Machines
Archimedes ARM2/3 MEMC1/1a VIDC1a IOC-A1 FDC1772
A5000 ARM3 MEMC1a VIDC1a IOEB [1] FDC711
Development Machines
Vic20 ARM3 MEMC1a VIDC20 IOC-A1 FDC1772
Vicky ARM600 [2] MEMC1a VIDC1a IOC-A1 FDC1772
Finished Machine
Omega/Medusa (Risc PC) ARM600 [3] MMU VIDC20 IOMD FDC711 [4]

[1] The IOEB architecture on the A5000 has an IOC as well.

[2] This machine has a MEMC1a, so the ARM could be a 600 (without a MMU) or a 610 where the on-board MMU is not being used.

[3] This machine has a MMU, so will be ARM610.

[4] It appears that RISC OS source used FDC711 as a switch for any PC style superIO chip, in the Risc PC's case it was a SMSC FDC37C665GT.


These 2 machines seem based on the A540 architecture (rather than A5000), and would have been used testing of the new VIDC20 graphics chip.

It's possible given the socketed nature of the VIDC1 on the Archimedes series, that these machines used a small board to (due to the VIDC1 and VIDC20 using different pin outs) that plugged into a regular A540.

I have no information as to what happened to these systems.


This machine also seems to be based on the A540 architecture. It would have been used to test the initialisation and reset code of the new CPU type and any changes that the ARMv3 architecture would have brought.

Information from sources online indicate this was a ARM600 card that plugged into the A540 CPU slot. This machine is said to now belong to Dave Walker formerly of Acorn.

Picture taken at Wakefield 2001 show, courtesy of IanS on Stardot.

If anyone has anymore information about any of the systems listed on this page please get in contact.