Looking for info on National Semiconductor RAM board (VAX 11/730)

tony duell ard at p850ug1.demon.co.uk
Sun Jun 21 12:08:22 CDT 2015

> >  Pressing the
> > button turns off the yellow LED and completely disables the board. Quite why you'd want to do this I do
> > not know...
> The reason you'd want a button to disable the board is when running
> diagnostics, you can "remove all the non-DEC memory" without
> physically removing it.  Of course it still could be the source of a
> problem, but at least operational memory boards can be "deleted" so
> they don't grossly affect the diagnostic code.
> It's a "feature" to allow customers to buy less-expensive RAM and
> still have a way to pass diagnostics without fingerpointing from DEC
> about that "other" board in there.

How would DEC know? These boards do not, AFAIK, have any form of machine-readable
ID. All DEC could tell remotely was how much RAM was in the machine. 

And I would hope any Field Servoid could spot a non-DEC memory board if he was looking
in the cardcage!

Disablng the board would prevent it acting as a data storage area, but if there's a shorted buffer
or something it could still mess things up. There is a common bus to all the memory boards, at least
in the 11/730. And I know the machine will not behave normally if there are gaps in the physical memory
space, quite whether it would run diagnostics in that case I do not know. So I guess you had better have all
the DEC boards at the start of the memory space and if you want to make the 3rd party RAM disappear, 
disable all the boards.


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