From owner-freebsd-stable  Fri Oct  8  2:35:39 1999
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To: David Malone <dwmalone@maths.tcd.ie>
Cc: Matthew Dillon <dillon@apollo.backplane.com>,
	Adrian Penisoara <ady@warpnet.ro>, freebsd-current@FreeBSD.ORG,
	freebsd-stable@FreeBSD.ORG
Subject: Re: [Patches avail?] Re: MMAP() in STABLE/CURRENT ... 
In-reply-to: Your message of "Fri, 08 Oct 1999 10:12:17 BST."
             <19991008101217.A24152@gosset.maths.tcd.ie> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Fri, 08 Oct 1999 02:34:25 -0700
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>On Thu, Oct 07, 1999 at 10:09:23AM -0700, Matthew Dillon wrote:
>
>>     Intel's ECC implementation is not perfect (1), but it's good enough to 
>>     catch these sorts of problems.
>
>Just as an interesting side note, we had a motherboard which
>supported ECC ram and had ECC ram in it and which was crashing.
>Eventually we discovered that every 8th byte in page aligned 4KB
>chunks was becomming corrupted.
>
>We replaced the ram and saw no improvement, and then got a replacement
>motherboard. As far as I could see the only significant difference
>between the new and old motherboard was the addition of a heat sink
>to the memory controler chip. The machine is now perfectly happy.
>
>So it seems that ECC isn't enough if your memory controler is too
>hot!

   ECC doesn't protect against certain types of motherboard address line
errors (since although the ECC is correct, the selected address is wrong, so
thus the data is wrong). There's parity protection on parts of the CPU
address bus, but I don't believe there is any protection between the memory
controller and the DIMMs for this type of problem. A handful of metal
filings is also known to cause problems when it is dispersed properly. :-)

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project - http://www.freebsd.org
Creator of high-performance Internet servers - http://www.terasolutions.com
Pave the road of life with opportunities.


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