> From: kpneal@pobox.com
> Date: Fri, 27 Dec 2002 17:35:41 -0500
> To: port-alpha@netbsd.org
> Subject: Memory: Parity vs ECC?
> 
> Say, if I'm trying to buy ECC memory for my AlphaStation 200, will any
> 1234x36 SIMM work? (Well, 64MB or smaller I guess.)
> 
> I thought non-parity was FOOx32, parity FOOx33, and ECC FOOx36. Is
> that not correct? It's pretty easy to find "parity" FOOx36 memory,
> but I really want ECC. What's the scoop?

Doesn't the memory controller in the Alpha use 8 bits out of 72
as ECC on a 64-bit word?  Just like a VAX memory controller uses
7 bits out of 39 as ECC on a 32-bit word.

It is a useful coincidence that 8 bytes of memory with one parity
bit per byte is just enough for single-error-correcting ECC of a
64-bit word.

    carl
-- 
    carl lowenstein         marine physical lab     u.c. san diego
                                                 clowenst@ucsd.edu