P800 boards

On Tue, Jun 12, 2012 at 4:06 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote: Yes. At the very least, the KA730 (11/730 and 11/725) and KA750 (11/750) used 39-bit-wide main memory. The 11/750 could take either 256K boards that also worked in an 11/70, and the 1MB boards fit in all 11/730s and most 11/750s (the earliest models needed an extra refresh wire strung along the memory backplane and an upgraded memory controller or else they could only take the 256KB boards). I never owned/ran the last rev of the 11/750 that had yet another memory controller and could take up to two 4MB boards, but I have no reason to believe they were not also 39 bits wide. In thousands of hours of running that variety of memory board (a couple square feet of 4164s for the 1MB model) in several machines, I think I only ever saw one or two hard failures (double-bit errors). I think we saw less than one correctable error per year. It was not frequent. -ethan