AM2+ CPU - 1 DIMM Per Channel

[scottw182]

I'm trying to choose the RAM for my new build and I'm getting confused. I'm getting an AM2+ processor, the Athlon 64 X2 7750, so I'll be able to use 1066 RAM. I'll get one of two boards, depending on available funds at the time of purchase, either the ASUS M3A78 or ASUS M3A79-T Deluxe. Both boards support AM2+ processors and DDR2 1066. Other, similar boards specify "Due to AMD CPU limitation, DDR2 1066 is supported by AM2+ CPU for one DIMM per channel only" in the product description on Newegg. This creates a problem for me because I was planning on getting 4 x 1GB modules.

I've been googling like crazy and have yet to find 2 responses that match up. One person says they have successfully used 4 x 1GB 1066 modules, set them to 1066 manually in the BIOS, and CPU-Z shows them as running dual channel. Another says you can run 4 sticks, but they will run single channel, not dual channel. One says you can run 4 sticks, but it will clock them down to 800, or less (another person said that this can happen anytime you run 4 sticks, not just if they're 1066). I've also read that it is a limitation of certain chipsets, or of certain motherboards, not of the CPU.

I've started to lean towards getting 2 x 2GB modules, that way I still have room to expand to 8GB in the future. But, further expansion wouldn't be an option if I can't use more than 2 modules.

If anybody could shed some light on these issues, I'd appreciate it. Feel free to school me on all of it, because I am just thoroughly confused.

[muddocktor]

Look up or download the memory QVL (qualified vendor list) for either of the 2 boards you are interested in and check and see what configurations they have tested it in. I know that the M3A79-T Deluxe shows a QVL on the ram in the book that comes with the mobo.

EDIT: I just d/l'ed the M3A79T QVL and it shows many different 1066 models on the QVL list, but there is a note that the 1066 ram with 4 modules is an AM2+ processor limitation. But you should be able to run 4 modules at DDR2-800 speeds with tighter timings. Either way, you won't notice a performance difference in real life situations, just maybe in synthetic benchmarks. And go with the 2 X 2 GB kits for your ram as you are much more future proof and the price difference is minimal.

[scottw182]

Thanks, I checked the QVL. Based on that, and a little more research, it looks like you're definitely right. DDR2 1066 is only supported for 1 DIMM per channel, or 2 modules. You can run 4 modules, but they're going to clock down to 800. You can then possibly go in and manually set them to 1066. If my system allowed me to manually set them to 1066, would that be ok to do or should I avoid it? Technically, that's "out of spec" so I don't know, what do you think?

I'm going to go ahead and get the 2x2GB Corsair Dominator TWIN2X4096-8500C5DF. That's the set I was already looking at, and luckily, it was one of the few memory sets on the QVL so I know they'll work.

[bigbuddy]

Phew.. am still confused.. When u say, it supports only for AM2+ processors, does it mean that AM2+ processors can have more than one 1066 RAM per channel?
Simply put, Am planning for Phenom II X4 and ASUS M4A78-EM. Please suggest the best mode to reach the 8GB mark in RAM config.

[steelnoles]

I am new to posting to the forum but have read the forums for a while. I have a problem. I am building an HTPC. My MB is a Gigabyte MA78GM-US2H. My CPU is an AMD Phenom X3 8750. I am using 2 1GB GSkill DDR2-1066. I am trying to install Windows XP Home. The reason for XP Home is that I just want to make sure everything is working before I buy Windows Vista since I have the Windows XP disk from a computer I built a while back and do not use. I have formatted a Seagate 300Gb Sata HD for a clean install. BIOS sees the HD. When I am installing Windows and I get to "The following list shows the existing partitions and unpartitioned space on this computer" there is nothing listed. As soon as I hit a button on the keyboard, I get a BSOD Stop 0x00000050.

I checked the Gigabyte website and it says that "Due to AMD AM2+ CPU limitation, DDR2 1066 or above speed is only supported by 1 DIMM per channel". The memory has been downclocked to 800. I removed one stick so only one stick is attached. I get the same problem. I do see that in the QVL, GSkill is not listed. Could this be the problem? I appreciate anyone's help here.

[CharlieCS]

Hi steelnoles welcome to the forum, try posting in General Hardware section of the forum and make a dedicated thread u will get some help alot faster , as to your problem you shouldn't be getting that error.Try different slots with only one stick of memory and try both sticks , make sure all your sata connection are tight .

[steelnoles]

Thanks, I will post there.

[ovybox]

I am new to posting to the forum but have read the forums for a while. I have a problem. I am building an HTPC. My MB is a Gigabyte MA78GM-US2H. My CPU is an AMD Phenom X3 8750. I am using 2 1GB GSkill DDR2-1066. I am trying to install Windows XP Home. The reason for XP Home is that I just want to make sure everything is working before I buy Windows Vista since I have the Windows XP disk from a computer I built a while back and do not use. I have formatted a Seagate 300Gb Sata HD for a clean install. BIOS sees the HD. When I am installing Windows and I get to "The following list shows the existing partitions and unpartitioned space on this computer" there is nothing listed. As soon as I hit a button on the keyboard, I get a BSOD Stop 0x00000050.

I checked the Gigabyte website and it says that "Due to AMD AM2+ CPU limitation, DDR2 1066 or above speed is only supported by 1 DIMM per channel". The memory has been downclocked to 800. I removed one stick so only one stick is attached. I get the same problem. I do see that in the QVL, GSkill is not listed. Could this be the problem? I appreciate anyone's help here.

I remember when I downgraded my laptop to XP tat I had to insert SATA drivers in XP because it does not have it. My best bet is that is your problem, not the memory.:santa2:

[trents]

Stellnoles,

Windows XP does support SATA natively if you have a version which includes the later service packs. The original version before service packs did not. If you have the early version XP then you may be able to get a SATA driver from your mobo manufacturer and install it on the hard drive first with a or thumb drive. It might even already be on the install disk that came with the board. Usually, though, this is only a problem with older motherboards when SATA first debuted. The ones made in the last several years seem to take care of that apart from the OS.

[Malakai]

Simply, if you try to run 4 sticks of ddr2, on most any platform, you wont be able to run ddr2 at 1066. The memory controllers on the cpu's just cant handle the load. A few people get lucky, but for the most part, your going to be stuck running @800mhz 4-4-4-12 instead of 1066 5-5-5-15. Its really not a big deal. I got mine up to 1000mhz 5-5-5, which is plenty close to 1066 :)