[Info-vax] DEC Multia (UDB) issues

[Steven Schweda]

On Oct 17, 6:43 pm, John Wallace <johnwalla... at yahoo.co.uk> wrote:

> Some AlphaStations started life with parity memory and it shipped as
> 36bit parity (aka longword parity).
>
> Then some HQ genius spotted that in a 21064-based AlphaStation you
> didn't need all 36 bits. Because all memory reads and writes were
> longwords or wider, you only needed 33bit memory to make it parity
> protected. [...]

   Really?  The oldest/lamest Alpha system I ever used was an
AlphaStation 200 4/233.  Its approved memory was fast-page
mode, parity.  (According to its "User Information" book,
"The system requires 72-pin parity SIMMs that have an access
time of 70 ns (nanoseconds) or 60 ns.")  But those extra
"parity" bits were aggregated for use as ECC, not for simple
parity.  One extra bit for each eight data bits means four
extra bits for a 32-bit word, which is enough for ECC.  The
last VMS system I saw which used parity memory as parity
memory (and not as ECC memory) was a MicroVAX II/III or a
MicroVAX/VAXstation 2000.  I've never seen any machine which
used standard parity SIMM/DIMMs as anything other than ECC.

   I don't get around much, so perhaps someone, somewhere,
really did use some non-standard, parity-only,
wider-than-8-bits, memory module, but I've never seen one,
and I wouldn't credit such a claim without some better
evidence than a vague recollection.