Date: Mon, 24 Sep 2001 17:58:59 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: ecc on i386 Message-ID: <200109250058.f8P0wx998146@earth.backplane.com> References: <15279.54029.454089.299807@grasshopper.cs.duke.edu>
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:What happens on an ECC equipped PC when you have a multi-bit memory
:error that hardware scrubbing can't fix? Will there be some sort of
:NMI or something that will panic the box?
:
:I'm used to alphas (where you'll get a fatal machine check panic) and
:I am just wondering if PCs are as safe.
:
:Thanks,
:
:Drew
ECC can typically detect and correct single bit errors and detect
double bit errors. Anything beyond that is problematic... it may or
may not detect the problem or may mis-correct a multi-bit error.
An NMI is generated if an uncorrectable error is detected.
On PC's, ECC is optional. Desktops typically do not ship with ECC
memory. Branded servers typically do. A year or two ago I would
have been happy to use non-ECC rams (finding bad RAM through trial
and error), but now with capacities as they are and memory prices down
ECC is definitely the way to go.
Bit errors can come from many sources, memory being only one. Bit errors
can occur inside the cpu chip, in the L1 and L2 caches, in memory, in
controller chips... all over the place. Many modern processors implement
parity on their caches to try to cover the problem areas. I'm not sure
how Pentium III's and IV's are setup.
-Matt
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