Talk:MicroVAX I

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Spec differences?

The old content had ram = 1 MB, and year introduced = 1984; not sure which is correct. Jnc (talk) 15:36, 29 July 2017 (CEST)

The MicroVAX I Pocket Service Guide (EK-KD32A_PG-001, Aug 1984) says 3MB if you fill all six slots with memory but in practice you need peripherals, so four slots of memory (2MB) is a practical limit. That's using MSV11-P boards. The Supermicrosystems handbook says that the KD32-AA has a limit of 4MB (which I think is an architectural limit based on the amount of memory possible on the Qbus). MSV11-Q memory boards had more capacity but I don't have an old enough Systems and Options catalogue to know whether they were supported in the uV1. So 1MB is, I think, wrong. 3MB is certainly possible but (in 1984) impractical. 4MB seems quite plausible to me but I don't have a cast iron reference (yet!). As for 1984, the earliest manuals have that date. ComputrWorld June 18 1984 carries a feature on p 58 or so. So announced in 1983 and shipped in 1984 does sound right. Somewhere or other I know there is a write-up of the story behind the uVAX I, but I don't seem to have it to hand. Antonioc (talk) 20:58, 29 July 2017 (CEST)

MSV11-J versions

Which versions work in the MicroVAX I? The -JB/-JC apparently have bugs in their QBUS support, so they only work in the PDP-11/84; the -JD/-JE will work anywhere. Jnc (talk) 13:05, 16 June 2022 (CEST)

The MicroVAX I can only use QBUS memories, or QBUS-compatible memories (like the MSV11-JD/-JE), so the -JB/-JC will most probably NOT work.
My own MicroVAX I is running with a MSV11-JE 2 MB board in slot 3. Vaxorcist (talk) 14:01, 16 June 2022 (CEST)
OK, thanks for confirming that.
Micronote 28 does say "[the -JB and -JC] modules can not be used in a Q-bus system due to gate array incompatibilities", which I take to mean 'MSV11-JB/-JC cards don't work on the QBUS'.
I recall reading someone's report, which I just tried to search for, but cannot find, that they tried to use a -JB/-JC in a PDP-11/83 (I think), and it damaged the file system. This makes sense, if the problem as is it is described, since in an /83, the CPU will use PMI to talk to the MSV11-J, whereas DMA devices will try and use the QBUS - but in the /84, both CPU and DMA will use PMI (the DMA via the KTJ11-B). Jnc (talk) 19:09, 16 June 2022 (CEST)