linux-kernel - Re: BIOS detects 4 GB RAM, but kernel does not

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Message-ID: <p73bqr83vco.fsf@verdi.suse.de>
Date:	30 Jul 2006 00:21:59 +0200
From:	Andi Kleen <ak@...e.de>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	iforone <floydstestemail@...oo.com>, linux-kernel@...r.kernel.org
Subject: Re: BIOS detects 4 GB RAM, but kernel does not

Robert Hancock <hancockr@...w.ca> writes:

> Athlon 64/Opteron CPUs have support for moving this part of the RAM
> above 4GB to allow it to be used. This is part of the CPU's on-die
> memory controller so no special chipset support is needed.

In cheap boards >3.5GB RAM configurations are usually not officially
supported by the vendor (= not tested) and there are systems where it
doesn't work when enabled in the BIOS (doesn't work = kernel crashes
randomly when accessing bad memory ranges)

I guess it's a subtle hint that above 3GB of RAM you should be using
ECC DIMMs anyways, which need a more expensive workstation class
board.

-Andi
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