Simtec 300/400 series 4-8MB RAM upgrade

The Simtec 4-8MB ROM RAM board gave Archimedes owners the ability to double the amount of RAM that an Archimedes could support. The memory limit for the Archimedes was defined by an architectural limit of the MEMC chip in that it could address a maximum of 4MB of RAM. The designers at Acorn foresaw that the 4MB limit may be a restriction and so designed the MEMC chip to be able to work in concert using a maximum of 4 MEMC chips providing support for a total of 16MB of RAM.

The Simtec upgrade consists of two carrier boards. The first being the MEMC controller board which requires that the Archimedes' on board MEMC controller is removed from its socket and placed in one of the two sockets on the board. The board then plugs into the empty MEMC controller socket on the motherboard.

The MEMC carrier board is connected to the ROM RAM carrier board by way of a ribbon cable. The first bank of 4MB controlled by one MEMC chip resides on the Archimedes motherboard, the second MEMC chip controls a bank of 4MB which is located on the ROM RAM carrier board. The additional RAM is delivered by several low profile RAM chips which are obscured by the RISC OS ROMs in the photo below.

Looking at the Archimedes motherboard in full, you can clearly see the on board 4MB of RAM on the right of the picture. The MEMC controllers are then located to the left of the RAM and are connected by the ribbon cable to the RISC OS ROM RAM carrier board where the second 4MB of RAM is located.

The only production Archimedes that Acorn developed which could support a full 16MB of RAM natively was the A540/R260. All other Archimedes machines were stuck with a 4MB maximum limit unless a third party upgrade such as the one detailed here was used. Most if not all upgrades provided support for the addition of only one extra MEMC chip allowing for an increase of the limit of available RAM to 8MB.