The last Acorn machine I wrote anything for was the RISC PC, which I think was ARM6, if I remember right. So, I lucked out: first Archimedes: ARM2, last one: ARM6 then done :D
Depends which model you had, I think. The 1994 model had the ARM610, updated to the ARM710 in 1995. I'd forgotten that the ARM7 series implemented two different instruction sets, though. The ARM710 had the same instruction set as the ARM610, with ARM7TDMI coming along slightly later.
