There's also the question of what the memory bus on each VAX implementation can handle. I forgot the 780 answer but chances are its address bus width is not nearly enough to support 512 MB. paul
Apologies if this is a repeat but I got a bounce from the list. I
had written:
[
I have 64MB as the maximum memory for the VAX-11/780, but I
didn't record where I found that, so I have no idea how reliable
it is. Wikipedia has 128MB and they've referenced it, but it's
basically the SIMH documentation so it certainly doesn't mean that
you could ever configure that much memory on a system. The
MS780-E/F memory subsystem brought the VAX-11/780 up to 16MB (or
maybe 32MB if you could fit two of them in there). There was a
later MS780-H and the FMPS suggests that it could control 40MB, so
you'd think that you could get to 80MB that way. But the 1986 VAX
Hardware Handbook says that with the MS780-H you could only get to
64MB. It explicitly says that the MS780-E controlled up to 16MB of
memory and that you could fit a second MS780-E to get up to 32MB.
There's no mention of a second MS780-H.
To answer the "what could I have physically configured using DEC parts in 1983/4" I think you'll need a Systems & Options Catalogue from that era.
]
But after sending that I read a bit further in the Hardware
Handbook and found:
"The 28-bit SBI longword address field allows access to up to 512
Mbytes of
main memory. The hardware supports a maximum of 64 Mbytes of main
memory. Physical memory operations are performed when bit 27 of
the SBI
addresses is zero; 1/0 operations occur when bit 27 is one.
So SBI could do 256MB of which half was for I/O."
So there seems to be something that caps physical memory at 64MB
(plus perhaps a bit for multiport memory, but that was always just
a handful of MB).
Antonio
-- Antonio Carlini antonio%acarlini.com@localhost