R260 CPU and RAM cards. The CPU card at the bottom right is a 30MHz ARM3. Above it is an Acorn 4MB RAM card with a MEMC1a. On the left are 2 Simtec 4MB RAM cards each with its own MEMC1a. The R260/A540 was designed with 4MB on the motherboard and could take up to 3 4MB RAM cards, each with its own MEMC1a, because the MEMC1a can only address 4MB RAM. It has been reported that the RAM cards need to be matched, preferably from the same batch, but I have found no problems mixing Acorn and Simtec cards.
I have also tested the R260 with a different CPU card with a 26MHz ARM3 and an FPA10. This worked without problems and the benchmarks showed that Dhrystones/sec fell to 22621, but kWhetstones/sec rose to 2807. If I had RISC iX on this computer it would probably benefit from the FPA.