I'd like it if anyone can shed some light on the issue for us newer members... If I go to the boneyard and find a 7749 ECM from a Quad-4, it will have a 256k prom in the carrier. If I get a 7749 from a Turbo Sunbird, it will have a 128k prom... How does the ECM know where to load the prom into memory? It the answer in the other chip(s) in the carrier? Thanks, Mike V