It's down to either the KIM-1 or the JOLT. The JOLT was advertised in December 1975 ( http://retro.hansotten.nl/6502-sbc/jolt-and-super-jolt/jolt/ http://retro.

It's down to either the KIM-1 or the JOLT. The JOLT was advertised in December 1975 ( http://retro.hansotten.nl/6502-sbc/jolt-and-super-jolt/jolt/ http://retro.hansotten.nl/6502-sbc/jolt-and-super-jolt/jolt/ ), compared with the 6502 which was being sampled around June or July. The KIM-1 was variously noted as early as winter 1975 but some sources say it wasn't available until 1976, but then the JOLT probably didn't get into people's hands until then either. I think it's logical that MOS would have been the first one to use their own chip but that's not a given. I have a ROR-less KIM-1, though, so there are systems dating from that early.