I did a search but couldn't come across any topics that address my problem.

I built this pc back in July (07) with a Patriot 2GB kit (PDC22G6400LLK) and running Windows XP and all was well.
I recently decided to add another HDD and installed Vista on it to run dual boot. I also purchased a second Patriot 2GB kit (again PDC22G6400LLK) and installed it.
The problem is that while my BIOS and CPUID will both recognize 4GB total memory, either OS will only recognize 2GB. I've tried every configuration of the modules that I can imagine, I've tried setting the timings manually in BIOS, I've tried using only one module, two modules, three modules, and all four, and it still only reads 2GB (Windows XP lists as 2,096,412 KB and Windows Vista lists as 2047 MB). I know that neither OS is probably going to show me the full 4GB, but I believe that it should show more than 2.0 GB. Anyone have a clue as to what could be the problem here? Thanks.

PC Specs:
Antec Nine Hundred Case
MSI P6N SLI Platinum
Intel Core 2 Duo E6600
Artic Cooling Freezer Pro
Patriot EP 2 x 2GB(2x1GB) DDR2 800 PC2-6400
2 (SLI) EVGA GeForce 8800 GTS 320MB
Creative SB X-Fi Platinum Fatal1ty Champion
WD Raptor 150GB
WD Raptor 74GB
WD Caviar 500GB
LiteOn DVD burner LH-20A1H-184
ASUS DVD-ROM DVD-E616A3
Apevia Iceberg 680w PSU
Windows XP Pro SP2
Windows VISTA Ultimate
(Dual Boot, OS’s on separate drives)

first thing, make sure memory remapping is disabled in bios

Thanks for the quick response.
I've looked but I can't find anything in there do do with memory remapping, unless MSI calls it something else.

32 bits OS limitation. Max address space is 4 gb, so substract all the address needed to anything hardware you have, especially your 2 video card taking 640 Mb of adress space, then you come close to what you have now.

64 bits OS don't have such limitation. as their adress headroom is far greater.

I've just looked in the manual, and they don't touch that subject at all.

On Asus boards the remapping function remaps on a 1G-boundary. Which means that RAM above 2 or 3 GB will be lost, if you use 32-bit xp or vista.

screw what windows says it is, try SiSoft Sandra (www.sisoftware.net) and/or CPU-Z (www.cpuid.com)...

Also, you COULD try the /3gb switch, but that re-arranges the allocation from a 2/2 (user/os) config to a 3/1 and may actually slow performance...

here's a good read on the RAM limitations of 32-bit windows, as well as a really good read on the /3gb and even /pae switches...
http://www.dansdata.com/askdan00015.htm

good luck

pendejo

First of all, thanks for all the help guys.

OK, I've built several systems at work for softcad aerial mapping using 4GB memory, Quadro video cards, and 32 bit XP and they all show at least 3GB. That's what had me puzzled. I know that neither of my OS's can use the entire 4GB memory, but it just seems odd that no matter if I use 2, 3, or all 4 1GB modules, Windows XP lists as 2,096,412 KB and Windows Vista lists as 2047 MB. It doesn't change 1MB no matter how may I use.
I tried CPUID and it shows the exact amount total and in each slot with each configuration, as does BIOS.
I'm kind of wondering if I would get the same effect if I used 2 x 2GB modules.
I don't know, maybe I'm crazy, but it just doesn't seem right.

It's not right,Mine lists 3.25G's on XP home

boner,
Who are you calling that name. That kind of language is not allowed on this forum.

It all depend of how much hardware you have. he has SLI, with 2x320MB videocard.. If you have a, let say 128MB video card. then you have a 512 MB advantage on him.

they mention the remapper in their common faq:

http://global.msi.com.tw/index.php [...] t_id_page=

I believe PAE switch was disabled from SP1 onwards.

I just checked that, and there is no option to enable hardware memory hole as they described, also it is showing the full 4GB (or 2 or 3 depending on the number of modules) at post each time. I did find this in another FAQ, though it doesn't really help.
Question:
Why system couldn't be detected as 4G when each DIMM is installed with an 1GB memory module.
Answer:
Due to chipset limitation, your MB can't support memory Remapping function, we can only provide one item to show "Physical Memory Size" 4G. The "Available Memory Size" still will be lower than 4GB. Maybe 3.5/3.2…etc, so you can't get full 4G memory.

Just wanted to update you guys in case anyone else experiences the same problem (that's how we learn, right?).
Over the weekend I decided to use EVGA's "step-up" to upgrade the newer of my two 8800 gts's to the 8800 gtx.
I pulled the card and flopped the SLI switch on the motherboard to the non-sli side and rebooted.
To my suprise, Win XP now recognizes 3,144 MB of memory and Vista recognizes 3,071 MB.
The only thing I can figure is that because when my MB (MSI P6N SLI Platinum) is setup with two video cards, it splits the 16x available at the pci-e2 slot and runs both pci-e2 & pci-e4 slots at 8x.
Thought it might be handy to know for future troubleshooting.