4 GB RAM showing up as 3, BIOS memory hole and all that

Martin Cracauer cracauer at cons.org
Sun Sep 4 05:47:26 PDT 2005

David O'Brien wrote on Sun, Sep 04, 2005 at 01:36:52AM -0700: 
> On Mon, Aug 15, 2005 at 12:56:57PM -0400, Martin Cracauer wrote:
> > I have a Dual Opteron board with 4x 1 GB RAM.  The memory count in the
> > BIOS goes up to 640 KB + 3072 MB, and FreeBSD says it sees 3 GB.
> > 
> > I know/assume/heared this has to do with the I/O space placed in the
> > upper GB and that you can re-map the top GB to avoid the problem.
> ... 
> > Any way to get my GB back?
> Depends on the BIOS.  Some BIOS's have knobs for the "memory hole" and
> simply control how large the hole is.  Others have nobs for the "memory
> hole" that AMD internal often calls the better named "memory hoisting" -
> which is what you are asking for.  Revision E CPU's have better HW support
> for memory hoisting, but some BIOS's control of it are still buggy.

Thanks, David.

A BIOS update did indeed give me my top gigabyte back, sans 128 MB for
my video card.

Martin Cracauer <cracauer at cons.org>   http://www.cons.org/cracauer/
FreeBSD - where you want to go, today.      http://www.freebsd.org/

More information about the freebsd-amd64 mailing list