Re: Which ASUS mobos support memory hole remap?

Hi Chris -

Very early Athlon64 models did not support this feature, but the current releases all do. There are actually three parts to the problem, for the benefit of anyone reading this who's unfamiliar with it.

The root of the issue is that 32-bit PCs have traditionally used address space between 3 and 4 GB for devices and memory-mapped IO; not the actual memory, just the memory addresses. They have done so because that's the upper limit of a 32-bit processor's memory address range. Because of that, any physical memory installed in that address region is invisible. For compatibility's sake, that convention has carried over to 64-bit processors, even though they are capable of addressing far more memory.

To get around it, the first thing you need is a chipset and processor that support memory hole remapping; the "memory hole" being that invisible region occupied by devices. Basically, addresses from above the memory hole are mapped into those addresses for the benefit of the software.

Even with supporting chipset and processor, the BIOS has to provide the option to turn the feature on. Many early BIOS didn't provide it, even with chipset and processor support.

Finally, you need a 64-bit operating system. WinXP, for example, is a 32-bit OS, so regardless of the BIOS settings, it is incapable of addressing anything over 4GB, and therefore still has to use the memory hole area for devices addresses. WinXP 64 or Linux for AMD64 fits the bill.

So, my search has been for a mobo with a supporting chipset (the entire nForce4 series, plus Intel 955X and 975X), AND a BIOS option to enable the feature. It's the BIOS part that I've had the hardest time determining, because the mobo manufactures don't provide enough detailed information.

Mark


Chris C wrote:
Hi, as far as I understand, being that socket 939's use AMD's. The memory controller is actually on the PCP, thus the issue may well be with AMD and not the motherboard manufacturer....
ChrisC
"Mark Baker" <mark.baker2@xxxxxxx> wrote in message news:Bctbg.659$sP1.199@xxxxxxxxxxxxx
I finally called ASUS tech support, and they can't even tell me for sure. The best the guy could do was, "it should work". Kind of pathetic, really.

I know their SLI X16 based mobos support memory hole remap OK, but I have no need for SLI and don't want to spend the extra money for it. I guess I'm going to buy an MSI K8N Neo4, since I've been able to verify that it works like I want it to.

Thanks for your help,
Mark


Paul wrote:
In article <x2obg.644$sP1.352@fed1read07>, Mark Baker
<mark.baker2@xxxxxxx> wrote:

I'm looking for a socket 939 mobo that will allow me to use a full 4GB of RAM in a 64-bit OS. I'm familiar with the problem; most chipsets use address space between 3 and 4 GB for devices. 32-bit OS's do the same thing, but a 64-bit OS will cure that part of the problem.

The documentation I've been able to find from the mobo manufacturers is confusing at best. I had a member of another forum recommend an nForce4 Ultra mobo to be based on his personal experience that it supports this feature, but the manufacturer's website seems to indicate that it doesn't. I think a lot of this manufacturer documentation is generic and doesn't necessarily apply to all products, but I need to be sure before I buy.

My understanding is that all the nForce4-series chipsets support memory hole remap, but the ASUS FAQ I've found on the subject only mentions the SLI X16.


So, the twenty-dollar question is, which ASUS socket 939 mobos provide a BIOS option for memory hole remapping?

Thanks,
Mark Baker
Try a generalized search. Use your favorite search engine and enter
terms like "a8n-sli memory hole" and you should see instances where
people discuss this setting in their BIOS. Try the search with whatever motherboard you are interested in.

http://www.altavista.com/web/results?itag=ody&q=a8n-sli+memory+hole&kgs=1&kls=0

The trend seems to be, that memory hole support is not in the first
released BIOS, but may appear in subsequent BIOS releases. As a
result, the manual doesn't reflect the setting (as the manual
only shows the BIOS as it looks in the first release).

Paul


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