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Date: Wed, 15 Oct 2003 23:06:32 -0700
From: David Schultz <das@FreeBSD.ORG>
To: "Dag-Erling =?us-ascii:iso-8859-1?Q?Sm=F8rgrav?=" <des@des.no>
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cc: hackers@FreeBSD.ORG
Subject: Re: real vs. avail memory
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On Sun, Oct 12, 2003, Dag-Erling Smrgrav wrote:
> I've gotten used to the fact that there is a small discrepancy between
> real and available memory, but I was surprised to see the following in
> dmesg on a new P4 system:
> 
> real memory  = 1073676288 (1023 MB)
> avail memory = 1037799424 (989 MB)
> 
> That's a full 40 MB difference...  where does that memory go?  is it
> used for page maps or something like that?

Unless this is related to Peter's recent machdep.c changes, the
difference is probably just random chunks of memory that the BIOS
decided to use.  This could include a shadow copy of the BIOS, the
BIOS data segment, maybe a frame buffer for a cheap integrated
video card, etc.  If you do a verbose boot, you'll get a list of
the chunks of memory that are taken according to the BIOS.