--- Alan Perry <alanp_at_snowmoose.com> wrote:
> Finding this list has encouraged me to try and get some stuff together
> on my VAX...
> Q3. Right now the memory slots have M8750s CJs in both end slots and 6
> six National Semiconductor 753 1M boards in between. Does it have to be
> this way? I have two spare M8750s. Are there any advantages between
> the DEC memory boards and the NS boards?
The only advantage in the old days was that 3rd-party memory boards were
substantially cheaper, but OTOH, DEC FS could decline to service your
machine unless it was 100% DEC
I don't know the NS boards by number, but I know that some later 3rd
party boards used 41256 chips rather than 4164 chips - 25% of the power
consumption. Won't matter lots and lots in an 11/750, but it made
our 11/730 run cooler.
If you happened to replace all 8 1MB boards with newer ones, I could
imagine that the drop in power consumption would be noticable on your
monthly electric bill (presuming you leave your 11/750 on 24-7).
Armed with schematics (originals or reverse-engineered), one could
conceivably remove the 41256s from one of those 3rd party boards (EMC?)
and dead-bug some 44256s in there. Having moved from two banks of 4164s
to 2 banks of 41256s to 4 banks of 44256s with the same DRAM controller
chip (74S409) in the COMBOARD line (128KB -> 2MB), I know that you can
make that subsitution in a robust memory design (ECC bits notwithstanding).
DEC 1MB memory cards had 156 4164s (39-bits wide, 4 banks x 64Kbit = 256KW
with ECC). The EMC(?) card I'm thinking of was 75% bare and had two rows
of 41256s chips (39 DRAM chips in total). If one could do the
substutition, it would have 10 44256s with one bit going to waste.
Considering that the 44256s we used with the VAXBI COMBOARD were 44C256s,
that's not much power at all, especially not compared to 150+ NMOS chips.
Not precisely original, but a lot cheaper than designing (and burning)
your own 1MB memory cards from scratch.
-ethan
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Received on Fri Dec 13 2002 - 05:08:00 GMT