

Acorn Risc PC (Prototype)

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I bought this computer in May 2005 on ebay from Uniqueway Ltd. Paul Middleton described it in the auction as:

 "This auction is for a very rare Acorn Computers - Risc PC prototype.
 It is clearly marked on the lid and on the Serial Number sticker as being a prototype.
 It is virtually identical to a production machine apart from a few small points.

  1. The podule support bars were coated with the EMI reduction paint coating, which was conductive and was found to short out certain podules. These were masked off from being coated in production machines.
  2.  The floppy disc is the same as an A5000 model and is not colour co-ordinated to the Risc PC casing.
  3.  The 2MB VRAM was produced on a PCB that was a bit too thick and consequently it is very difficult to extract.

It has a 70W power supply and is fitted with an ARM 610 card and RISC OS 3.5."

Documents and Manuals

I have no documents specific to this prototype. See Risc PC Computers  for other Risc PC documents.

 Risc PC (Prototype)

The Risc PC has an early Mark 1 Issue B botherboard and a low Unique Id (for a Risc PC). The Memory Controller is an IOMD20, rev B, unlike my other PiscPC 600s which have an IOMD21, rev A. The VIDC20 is marked "VY86C630 PROTO A".Similarly the I/O chip is an FDC37C665GT, rev 1, where as my other Risc PC 600s have an FDC37C665GT, rev 2.

The Acorn ARM610 CPU card  is a prototype, or pre-production, model with an GPS P611ARMPR clocked at 30MHz on an Issue C card. The "ISS. C" shows it is a prototype (or pre-production) because Acorn used issue letters for development hardware and issue numbers for production hardware.

I have also installed the Acorn "Duet" ARM610 2nd processor  which was used to debug the second processor connector but not sold as a commercial product.

 I have added a Fujitsu 200MB Hard Disc, because the original hard disc had been removed, and a TEAC CDROM, because a CDROM (or was it a 5¼" floppy/hard disc?) had been fitted at some time and later been removed. I am not sure I actually tested to CDROM as I don't think that RISC OS 3.50 supports them. I also added 24MB RAM, 1x8K and 1x16K SIMMs, as there there was no memory included.

I guess Acorn needed to provide prototype Risc PCs to their 3rd party hardware and software developers, so that they could test existing hardware and software on a Risc PC and modify it if necessary, and ensure the products were available at launch and certified to run on a Risc PC.

Here are some photographs:

Risc PC prototype front

 Risc PC Prototype (front)

  This is the front of the Risc PC showing the floppy disc drive which does not match the Risc PC case. It is a Citizen model used in the A5000 and looks as if it would match the A5000 colour scheme.

Risc PC prototype top

 Risc PC Prototype (top)

What makes me think that this is a pre-production, prototype, Risc PC? Well this is one of the reasons, it is painted on the top (lid) of the Risc PC. Can't get much clearer! Although I suppose it could be a hoax...

Risc PC prototype back

 Risc PC Prototype (back)

The back of the Risc PC, the podule blanking plates are missing, as is the blanking plate for the network interface. There is further evidence of the Prototype staus with the "PROTOTYPE" serial number and the missing barcode.

Risc PC prototype motherboard

 Risc PC prototype motherboard

In the middle at the bottom of the motherboard, the part number (0197,000 Iss B) is just visible. On the right hand side from the bottom are the 2 RISC OS 3.50 ROMs, the CPU connectors are next with the IOMD20 above them. The IDE connectors are visible in the top right. At bottom on the left is the VIDC20 with the VRAM immediately above. The CMOS RAM Battery is the middle on the left edge with the 2 RAM SIMMs next to it.  

Risc PC prototype VRAM

Risc PC prototype VRAM

 This is the VRAM module that Paul Middleton referred to in his description. It is very difficult to remove (or insert) the module from the motherboard. 


Unique identity00000050A401B34
Motherboard part no.0197,000 issue B
Motherboard serial no.n/a
CPU Card part no.0197,208 Issue C
CPU card serial no.ARM-1000117
CPU TypeARM610
CPU Clock


2nd Processor part No.0197,215 Issue A
2nd Processor serial no.P2-008
2nd Processor TypeARM610 2nd Processor Card
Memory ControllerIOMD20
0297,030 rev B
Memory Clock16MHz
Video ControllerVIDC20
Floppy Disc DriveCitizen OSDA-75E-U
Hard Disc Controlleron board IDE
Hard Disc Drive200MB
Fujitsu M2618T
CDROMTeac CD-56E-034-U
Backplane Modelnone
Backplane part non/a
Podule 0n/a
Podule 1n/a
Podule 2n/a
Podule 3n/a
OS Date18-Feb-94
SICK v1.22
ARMSi v4.0