At 02:38 PM 8/21/01 +0200, Michael Kukat wrote:
>Ok, first, you also need different memory cards, the MS670 isn't compatible to
>the MS690, i found this out a while ago. Maybe it's just memory timing, but i
>had no success interchanging memory boards between my /300 and /400 here.

Michael is correct here, DEC changed the way memory access was done in the 
KA675 and later and you will need MS690 memory. There seems to be some 
"MS680" memory that are 32MB versions of MS690 memory but they _only_ work 
on the KA675/KA680 and are not recommended. I've read various warnings etc 
about it in bits and pieces of documentation (especially in things like the 
VAX 4000/600 site manual)


Antonio Carlini wrote:
     >   The later NVAX systems used the MS690 modules and a
     >  slightly revised backplane. The later VAX 4000-300 systems
     >  also had that same backplane. The part number is 54-19354-01,

--Chuck

>Now the backplanes (looking below the memory slots):
>/300: PELE BACKPLANE, 5019353-01, K2-P1, 5419354, BE3-0
>/400: same as above, but "GS-2" instead of "BE3-0"
>home this can help you a bit. I don't know exactly if the 2 backplanes differ.
>...Michael

As far as I can tell they differ in the way the data and address lines are 
terminated on the memory bus.