AMD CPU limitation w/ DDR2 1066

[Drover]

I am about to build a new setup and found some comments in various sites about a limitation with AMD and the use of DDR2 1066. There appears to be some sort of limitation, but it is not overly clear to me what impact this may have. Here is what I plan to pull together:

- Antec Three Hundred
- AMD Phenom 9950 BLACK EDITION 2.6GHz
- ASUS M3A79-T Deluxe AM2+/AM2 AMD 790FX ATX AMD Motherboard
- Seagate Barracuda 500GB 7200 RPM SATA 3.0Gb/s
- EVGA 512-P3-N801-AR GeForce 8800 GT 512MB 256-bit GDDR3 PCI Express
- OCZ GameXStream 700W ATX12V SLI Certified CrossFire Ready Active PFC Power Supply
- Two: OCZ Reaper HPC 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) for a totla of 8gb
- Vista Ultimate 64bit
- ZALMAN 9500A 92mm 2 Ball CPU Cooler

Can anyone help shed some light on this?

[mr_raider]

People with Phenoms and early BIOS revisions had troubles with ddr2 at 1066, and downclocked it to 800. I don't know if it's been resolved. Check in the Gigabyte sub forum, since we are several 790 chipset users in their.

Mind you, ddr2-800 will be just fine for that build.

[uddarts]

4 sticks are also going to enter into the equation. it won't be a drop and go.


ud

[BWM]

Down-clocking of memory speed as the number of sticks increases has always been a normal property and DOES NOT indicate a problem. It is within AMD's publicly stated specs. It is a normal reaction to increasing load on the processor's on-board memory controller and the use of unbuffered memory sticks. Reference section 2.8 of the following AMD document.

BIOS and Kernel Developer's Guide (BKDG) For AMD Family 10h Processors

[Drover]

Interesting. If i am reading the matrix on page 65 correctly, it seems to suggest that the frequency drops down to 533 rather than 800 if i am using 4 dimms of 2gb each. Is that correct? Also, if so, does anyone see any issues with that and the remainder of the equipment (and software) i plan to use in the computer?

[BWM]

Interesting. If i am reading the matrix on page 65 correctly, it seems to suggest that the frequency drops down to 533 rather than 800 if i am using 4 dimms of 2gb each. Is that correct? Also, if so, does anyone see any issues with that and the remainder of the equipment (and software) i plan to use in the computer?

Correct. 800 or below, actually. Expect 2T with 4 sticks, which is normal. Also refer to tables 21 through 23 for the expected results/recommendations as they pertain to operation at 1T command rates. Further reduced clocks are to be expected (and normal) for 1T.

[Drover]

So, would i be on equal footing if i bought ddr2 800 and saved a little cash?

[BWM]

My recommendation is to achieve the total amount of memory you desire using two sticks. If you want to run 64 bit Vista then I'd advise 2 x 2 gig sticks of either DDR2-1066 or DDR2-800. You'll not notice a performance difference unless benchmarking.

[Drover]

Thanks. I may end up using this computer for video editing. should i move up from 4gb to 8gb?

Thanks for the help.

[BWM]

I'm not sure that 8 gigs would work but I would think that 4 gigs should be enough.

[Drover]

Ok. Thanks. I was planning on buying some G.SKILL 8GB (2 x 4GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400). Thoughts?

Why do you think the 8gb not work? Just curious as the board can support it. I have built a few computers, but am not an expert. I really would like to have some fun with it, but definitely do as much up-front homework to avoid any obvious issues.

[Drover]

Depending on your ultimate RAM recommendation, i was thinking perhaps this might be a nice set-up.

- Antec 900
- AMD Phenom 9950 BLACK EDITION 2.6GHz
- ASUS M3A79-T Deluxe AM2+/AM2 AMD 790FX ATX AMD Motherboard
- Seagate Barracuda 500GB 7200 RPM SATA 3.0Gb/s
- EVGA 512-P3-N871-AR GeForce 9800 GTX(G92) 512MB 256-bit GDDR3
- OCZ GameXStream 700W ATX12V SLI Certified CrossFire Ready Active PSU
- G.SKILL 8GB (2 x 4GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400)
- Vista Ultimate 64bit
- ZALMAN 9500A 92mm 2 Ball CPU Cooler

[tpflum]

Recently, I put together a system with an Asus M4A78 Pro, Phenom X3 710, and Kingston 4GB KHX8500D2T1K2/4G. I have not changed anything from the default and it runs very well (XP). I even had Windows 7 on it for a while.
Now I've put together an ECS A790GXM-A, Phenom X3 720, with same Kingston KHX8500D2T1K2/4G memory. It will boot with 1 stick (2GB) but gives a 'BIOS in this system not fully ACPI compliant' error with both sticks (4GB) installed while booting and halts. I put the memory and processor into the first system and it runs OK. Thinking I have a memory compatibility problem, I ordered Crucial CT2KIT25664AA1067 4GB kit which they guarantee to be compatible with the ECS board. Got the same result. Also I wasn't able to run the DOS or Windows version of BIOS upgrade software.
Kingston was no help. ECS didn't respond to my email. Crucial now tells me that the 790 chipset has problems with 8500 (1066) memory and to reorder 800Mhz memory.
At least one evaluation I found for the ECS board was running 4GB of high speed memory.
Now I don't know what to think. Any experience out there with these combinations?

[uddarts]

with one stick, manually set the vdimm to factory specifications.

in the timings area search out command rate and set to 2t.


see if that helps.



ud

[uddarts]

i found a review that shows the full list of timings and i don't see a command rate setting.

if you haven't already disabled the ecs splash screen and do so. then watch the first dos post screen for the memory at 1t or 2t with the memory running 533/1066/pc8500.


ud