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MB does not recognize all of the installed ram

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January 26, 2011 1:28:29 AM

Problem description: Last weekend I purchased all new parts and assembled my new computer build. When I installed all of the hardware and powered on the PC for the first time the BIOS immediately recognized that I had 6gbs of Ram installed. That was correct as I had 3x2gb DIMMS installed. Everything in BIOS checked out as it recognized all of my new hardware so I continued on with installing my OS. Installing a fresh OS onto the PC was the last thing I did that day, with no other changes or installs being done. At some point between then and the next day I noticed that upon my next bootup the BIOS only recognized 4gb of ram. I made no hardware changes within the computer during that gap between it recognizing 6gb then 4gb. After attempting to fix the issue with troubleshooting (as detailed next) to no avail I abandoned my efforts. Oddly, after that I booted up the PC and it recognized that I had the 6gb. But yet again, just the next day I booted up again and its back to 4gb.

Attempted fixes: I did the basic troubleshooting of testing each stick of ram in each slot on the MB in sequence then starting BIOS to see what it saw. Each of my 3 DIMMS were recognized correctly as 2gb each in each of the MB slots. Each combination of 2 sticks for 4gbs were also recognized in each slot. The only thing the BIOS apparently doesn't recognize is the full 6gbs. Oddly however the issue seems to be intermittent as the BIOS seems to sometimes, but rarely, recognize all 6gbs. Then its gone again. This doesn't seem to pertain to any specific combination of the ram as the same combination that sees 6gb soon again sees only 4. I also attempted to fix the issue by resetting the BIOS to default by using the MB jumper but this did not seem to have any effect.

I called ASUS tech support and they pleaded innocent saying it was a RAM problem. Then I called Corsair and the tech explained that this is apparently a known issue due some weird picky issues due to the combination of the MB/CPU Memory Controller/RAM that isn't due to any defective part, just that the RAM is oddly incompatible. He assured me that simply replacing the RAM would solve the problem, but made sure to assert that the RAM was not at fault and that it would most likely work in any other system. He explained that he doubted replacing the MB or CPU was necessary as they were not at fault either. Again, it's just one of those finicky things that is simple to solve. Before I do anything like that I would like a second opinion. Could it be a simple issue where changing the BIOS settings of voltage and frequency levels would fix the issue permanently or do I need to RMA the MB or something?

Recent changes: The computer is a new build. Only the OS was installed after assembly.

Operating system: Windows 7 64 Bit

System specs:
CPU: Intel 2500k
MB: ASUS P8P67 LGA
Ram: 3x2GBS of Corsair XMS3 DDR 3 1333
GPU: Nvidia 570 GTX

PS: I understand very little about navigating the BIOS so you need to hold my hand with instructions regarding it. :) 
a c 1155 V Motherboard
January 26, 2011 1:46:16 AM

3x2GB kits are designed for LGA1366 to run in triple channel, Having that ram installed in LGA1155 board means single channel when optimized performance would be running a dual channel setup. I would either get a forth stick or just run it on 4GB in dual channel, either 2 or 4 slots filled!
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January 26, 2011 1:51:00 AM

Is there any way to run the LGA1555 in triple channel then? I haven't heard anything about the chipset being unable to support just 6gb in 3 channels, in fact I have been told specifically that it can.

And why then does it sometimes see 6gb in BIOS?
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a c 1155 V Motherboard
January 26, 2011 1:56:29 AM

It can run 6gb but only in single channel mode! It does not support triple channel! If you are not doing rendering or encoding the system will be faster with 4GB of ram in Dual channel than 6GB in single channel. You might have to look in BIOS at your memory config and see what it is reporting the 4Gb at channel wise.
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January 26, 2011 2:11:27 AM

It can run 8gb in dual channel optimized though correct?
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a c 1155 V Motherboard
January 26, 2011 2:12:13 AM

Yes it can!
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January 26, 2011 2:16:12 AM

SO what was that about "finicky problems of compatibility" that the Corsair tech support told me about? Was it just BS where he didn't know what he was talking about?
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a c 1155 V Motherboard
January 26, 2011 2:19:17 AM

If he did not point out that you had a kit optimized for LGA1366 he did not know enough to be credible (my opinion).
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January 26, 2011 2:22:56 AM

Too bad there doesn't appear to be an option anywhere online to buy one stick of 2gb XMS3-1333. Know of any?
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a c 221 V Motherboard
January 26, 2011 3:22:25 AM

Do your 3x2GBS of Corsair XMS3 DDR 3 1333 adhere to Intel's Sandy Bridge memory module design specification of 1.5 Volt or did you get the old 1.65 Volt modules for the previous generation i5 & i7 processors?
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January 26, 2011 10:50:57 PM

1.5 volts. I just need to go back to micro center and return this 3x2gb package for a 4x2gb one.
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March 16, 2011 12:55:07 PM

pagal lavade
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!