Chuck Guzis wrote: I'm calling the D825 as being earlier as it was a vacuum-tube box, while the B5500 was solid-state. In any case, the design was probably much earlier than the B5500. The Fact Sheet for the BUIC claims: "Data exchange occurs simultaneously between any memory and any computer or input/output module." That could imply that although SAGE used them as backup, they weren't necessarily limited in that way. Anyone know for certain? Could both CPUs be running at once? --ChuckMy understanding was that they could and did and the results were compared real time.But I do have an off list friend who spent 6 years on SAGE sites. If no answer pops up, I'll write to him and let you know.By the way, Al recently gave him the tour of the Museum and he gave us a couple of hours on the SAGE activity around the Bay area. Fascinating.BillyBy the way, during your CDC years, did you ever work on the 160-G? It's memory/external buffer modules had nine way access and could work with up to nine CPUs. Since each memory was indepenent, that meant that all nine processors could be running out of the same memory or nine different memories at the same time. Made for some marvelous and hairy troubleshooting problems when memory conflicts occured.