Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
In article <11690m84nkrgv28@corp.supernews.com>, "Randy Starkey"
<andy.starkeyNOSPAM@NOSPAMvictorychurch.com> wrote:
> Hi,
>
> I have a new A8N-SLI Deluxe board with 4 gigs of memory installed. 2 pairs
> of Kingston 1gig matched kits. The bios reports 4 gig fine, but Windows XP
> will only report 3 gig.
>
> Anyone know why?
>
> Thanks!
>
> --Randy Starkey
Getting to use all the memory is actually pretty complicated.
In terms of the address space, the PCI/AGP/PCI-Express busses
all need some addressing space, out of the total available to
the processor. Typically, when some of these busses are present
in a system, they "punch" a hole in the address space.
On a pure 32 bit system, the maximum address space available is
4GB, and if you stick 4GB of memory in such a system, some of
the memory is ignored. If accesses are made to areas around
3.2GB or higher, up to the 4GB mark, those accesses point to
PCI/AGP/PCI-Express hardware devices.
Now, your system is a 64 bit system. If you have the right
version of BIOS flashed into the BIOS chip, there is a setting
that controls "memory hoisting". Memory hoisting lifts the
wasted memory, above the 4GB mark, and makes it possible to
have address space for system bus access, and all of memory,
available at the same time. I believe the system memory is
remapped (virtual memory space), so that the memory can look
contiguous.
The next issue, is at the OS level. There are various limits
as to what the OS will do, when memory is made available above
4GB. There is also an issue, with the split between user
space and kernel space. (Note - at this point, you may need
a server version of an OS, to gain access to memory above
the 4GB addressing mark, so there is no free lunch.)
If you use a /3GB option in boot.ini, I think that changes
the user/kernel split, to 3GB/1GB, instead of the normal
2GB/2GB split.
As well, there is a competing idea, which is the use of
addressing extensions, that make it possible to access
memory above the 4GB address mark. /PAE is an option you
would use, if a processor supported the PAE extension.
http://support.microsoft.com/default.aspx?scid=kb;en-us;268363
The bottom part of this post explains some of this better
than I can. You should also search the Microsoft KB for
info on PAE, AWE, /3GB and so on, to get the full story.
http://groups.google.ca/groups?threadm=2mfmc8Fmff71U1%40uni-berlin.de
Paying for an OS to make this happen, might cost more than
the memory you just bought. I believe there are some versions
of Linux that can provide an (almost) free lunch. Good luck
in your research - if you learn anything useful to future
4GB memory purchasers, please post back so all can benefit.
HTH,
Paul
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