On Wed, May 26, 2021 at 3:38 PM Jonathan Stone <[email protected]> wrote: > > two points: > > 1. MS650-AA 8mb modules from a KA650 will work in a KA640. They won't work > with a KA655 or a kA660 (or a KN210_. Those need the MS650-BA, or the 16MB > MS650-BB, or the third-party 32MB modules. So if your KA640 is dead and you > want to upgrade, you will likely need new memory, too. (You likely know this > already.) >
I've been wrong about that for several years. I have always assumed that an M7621 MS650-AA 8MB memory board was compatible with all of the M7620 KA650, M7624 KA640, M7625 KA655, and M7626 KA660 CPUs. I didn't realize until now that an M7621 MS650-AA 8MB memory board is only compatible with the M7620 KA650 and M7624 KA640 CPUs, and the M7625 KA655 and M7626 KA660 CPUs are only compatible with the M7622 MS650-BA 16MB memory board (or the less common MS650-BB 8MB version of the M7622). Unless I am also wrong about this, the M7622 MS650-B memory boards are compatible with all of the M7620 KA650, M7624 KA640, M7625 KA655, and M7626 KA660 CPUs. KA655 CPU System Maintenance, Order Number EK-306AA-MG-001 http://www.bitsavers.org/pdf/dec/vax/655/EK-306A-MG-001_655Mnt_Mar89.pdf Page 1-4 (Page 15 of the PDF) "NOTE: The KA655 CPU supports only the MS650-BA (16 Mbyte) memory module. The MS650-AA (8 Mbyte) is not supported because of its slower access speed." KA660 CPU System Maintenance, Order Number EK-398AA-MM-001 http://www.bitsavers.org/pdf/dec/vax/4000/EK-398AA-MM-001_KA660_CPU_System_Maintenance_Dec90.pdf Page 1-10 (Page 20 of the PDF) "1.4 MS650-Bn Memory Modules The MS650-BA and MS650-BB memory modules are quad-height, Q22-bus modules. Timing of the MS650-BA (16 MBytes) and MS650-BB (8 MBytes) modules is dependent upon the KA660 clock speed and CMCTL. The MS650-AA memory module may not be used with the KA660 system CPU."
