Subject: Re: Memory: Parity vs ECC?
To: Nathan J. Williams <>
From: None <>
List: port-alpha
Date: 12/28/2002 00:47:52
On Fri, Dec 27, 2002 at 10:01:44PM -0500, Nathan J. Williams wrote:
> Matt Thomas <> writes:
> > You want x36 FPM since the AS200 uses two bank as once so each 64bit
> > access has 8bits of parity which the APECS chipsets uses for ECC.
> My manuals are at home and I'm behind a slow net connection, but I'm
> reasonably certain that the AS200 memory system does *not* need or use
> ECC; I think it only needs 33-bit memory. The documentation of the
> machine check errors generated on that system is full of notations
> like: "37: ECC error. Cannot happen, hardware does not have ECC
> support."

I've been told that the AS200 can use either parity or ECC memory, but
there is no use of the ECC bits. 

My AS200 came with six sticks of parity memory. They don't work on
the AXPpci33 (of which I have three, two of which have a CPU). I
don't want to buy memory that I can't use in both types of machine.

So, if I understand correctly, the x33 and x36 memory is exactly the
same except the x36 has extra bits? The extra bits are used by the
motherboard (AXPpci33, for example) to generate ECC, but the memory
just holds extra bits. Meaning, so long as the memory is really
x36 I can use it in either the AS200 or the AXPpci33. 

Incidentally, where is machine check documentation available? I
tried getting AS400 machine check docs out of the DEC rep my employeer
keeps around, but all I got was kids-level "that means something didn't
work right"-type answers. "Like, no duh!" (This was back when 
AltaVista was cool and was running as a trial on my desktop.)

Thanks for the answers guys! (It's bed time now...)
Kevin P. Neal                      
           On the community of supercomputer fans:
"But what we lack in size we make up for in eccentricity." 
  from Steve Gombosi, comp.sys.super, 31 Jul 2000 11:22:43 -0600