Last year I built a Core i7 920 system based on the ASUS P6T Deluxe motherboard. I have 3x1GB of DDR3 (triple-channel configuration), but only 2GB is being reported by: Windows XP, CPU-Z, the BIOS. Is this a hardware problem, or is the third gigabyte of RAM being reserved by the system for video card-related stuff? The video card has 512MB of RAM.

I realize that 32-bit Windows XP is not the ideal operating system for more than 2GB of RAM, but from what I've read it should be reporting at least 2.5GB.


If the BIOS is reporting 2Gb, then it's a hardware or BIOS problem, nothing to do with XP.

First thing I'd do is try the RAM two sticks at a time to see whether they're all good. Second thing would be checking if a BIOS upgrade is available.

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    1/ press the sticks down firmly, to make sure they are properly installed. 2/ get 1 stick at a time to show up, by removing them all, and trying one by one. It's usually the simplest things, hence 1. – Alister Bulman May 3 '09 at 19:22
  • You can also try a memtest to check if everything is okay – setatakahashi May 7 '09 at 12:04
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    This answer was the closest to being correct, so points to you. I ran CPU-Z and it reported that Slot C1 was empty, so I opened the case, reseated the stick, and it's now coming up as 2.99 GB in WinXP and 3 GB in the BIOS. – Scott May 29 '09 at 3:06

Double check what the BIOS is reporting. I suspect that your memory is actually there, but remapped over the 4GB limit: a 32bit OS will be able to see only 2GB, the BIOS should report the correct amount of memory though.

Your memory map might something like:

0-2GB physical memory
2-4GB hole for MMIO
4-5GB physical memory

My P5B-E does the exact same thing, but I'm running a 64bit OS...

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I have used a XP Machine (32 bit) with 4 GB so i know that it supoprts upto 4 GB. since you are saying that BIOS is also reporting it as 2 GB , this should be a hardware problem, you probably need to test the slots or do some switching of the RAM modules to identify the faulty one.

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In the bios, there should be a setting for dual or triple channel memory.

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  • Sounds like he's probably using it, from his question. – chaos May 3 '09 at 18:50
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    With these boards, you can put in the 3 sticks of ram, leave it defaulting to dual channel and it will boot fine, just picking up 2 of the 3 sticks. – Ryaner May 4 '09 at 8:30
  • There is no BIOS setting; it's automatic. – Scott May 29 '09 at 3:04

Try enabling the /3GB switch in your boot.ini.


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    The /3GB switch is for Virtual Address Space for applications,not Physical Memory. If the Bios is not recognizing the memory, there is no point looking for it at OS level – Dinesh Manne May 3 '09 at 18:40

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