Why can I set two DIMMs to 1066, but not four?

[Mugsy]

After much searching online, many people seem to share this problem.

I have four identical 2GB sticks of OCZ Platinum DDR2-1066 DRAM (confirmed via various apps) in my rig. But BIOS refuses to run them at anything above 800MHz (Dual Channel 400MHz x 2.) At startup, Bios reports my memory is "DDR2-800".

Originally, I was running only two 2GB sticks @ 1066, but after adding two more sticks of identical memory, BIOS's "Auto" settings downshifted to DDR2-800. I have tried setting the BIOS values by hand, increasing Dram voltage to 2.1v, bumping the mem-clock speed to 533, etc and so on. The result is always the same: an unstable system that crashes within minutes.

It doesn't matter WHICH two sticks I use, as long as I'm only using two sticks of memory, I can run @ 1066. But never with all four installed, and I have no idea why.

When I run "MemSet 3.5", it shows two of my DIMMS running @ "127ns" and two running @ "75ns". Setting all four the same (both 75ns or 127ns) causes Windows to crash. Here is the information:

I've read plenty of other posts from people having nearly the same problem, but have yet to see anyone answer it. I've even tried overclocking my entire system to make up the difference, but that crashes too.

Anyone have an idea why this might be happening?

AMD Phenom II x4 920 (2.6GHz)
Gigabyte MA790GP-DS4H motherboard
four 2GB sticks of OCZ Platinum DDR2-1066 DRAM
1gb ATI Radeon 5850HD

PS: Another detail, if I use onboard video instead of my vidcard, all my ram will run @ 1066 just fine. :sarc:

 

[essenbe]

How about download CPUz and show screenshots of the board, memory and spd tabs for all 4 slots with all 4 dimms installed. On the spd tab, in the top left it lists which slot. Show a screenshot of all 4.

 

[Snakeyeskm]

It is not unusual for certain motherboards to have different memory performance, if all slots are utilized. To the best of my knowledge, pending bios updates, there is generally no cure for this type of problem.

 

[TBoyd]

I tend to agree with Snakeyeskm. With only 2 dimms filled, you can run at 1066, but many manufacturers don't advise the buyers that some boards will not give you that speed when all 4 dimms are filled.

If you can achieve 1066 with all 4 dimms, let us know. Maybe you can pull it off.

At any rate, there is more advantage to having more memory capacity vs. memory Mhz. I doubt that the speed difference will be that noticable.

 

[Mugsy]

Cpu-z

How about download CPUz and show screenshots of the board, memory and spd tabs for all 4 slots with all 4 dimms installed. On the spd tab, in the top left it lists which slot. Show a screenshot of all 4.

Sorry, I should have posted these earlier. Here are the CPU-Z readings of my current configuration. I read elsewhere that others had success with lower (than 1066) settings. I tried bumping the FSB to 225MHz (x4 for 900MHz) this morning and so far so good. But why can't I do the full 1066 the DIMMs are rated at?

(The bump in FSB speed boosts me from 2.8GHz to 3.15GHz. Nice.)

(all four slots read exactly the same, so there was no point in posting pics of all four.)

 

[Mugsy]

I tend to agree with Snakeyeskm. With only 2 dimms filled, you can run at 1066, but many manufacturers don't advise the buyers that some boards will not give you that speed when all 4 dimms are filled.

If you can achieve 1066 with all 4 dimms, let us know. Maybe you can pull it off.

At any rate, there is more advantage to having more memory capacity vs. memory Mhz. I doubt that the speed difference will be that noticable.

I actually found some very useful information here. Seems there is some sort of physical quirk with the Phenom-II's when using all four memory slots.

According to some, getting all four DIMMs to full speed isn't impossible, but difficult, and varies greatly upon your choice of motherboard.

But I've always been baffled by why I can clock all my DRAM at a full 1066 while using onboard video but not a separate vidcard. (The performance hit by not using my 5850 is FAR greater than the boost in mem speed, making it a loosing bargain.)

On many memory-intensive processes, the increase from 800 to 1066 provides a noticeable improvement without having to overclock the CPU, enough to make it worth pursuing. I don't game that much. More of a video editor.