Yesterday I installed 2 x 2gb DDR2 6400 (800mhz) Ram in my PC, It booted fine but when I ran CPU-Z or Sandra it showed it running at 667 (333 Mhz) rather than 800mhz. I contacted my Mobo manufacturer who asked if I had the latest BIOS so I updated it. I also installed the public RC1 of Vista SP1 yesterday and today out of curiosity I looked again at the CPU-Z ram timings only to see it running at 199 mhz (Sandra also shows this). I had two sticks of OCZ 4200 in before and they ran exactly as stated (533mhz). OCZ asked me to manually set Dram up in the BIOS and CAS timings to 5-5-5-18. They also suggested upping the Northbridge voltage to 1.4 and finally the DRAm voltage to 2.0. I did all this and no change at all. My Bios shows DDRII800 and Sandra says the MAX memory speed is 800 too. I loaded default settings in the BIOS and now I have 249 Mhz, so less than 500 total now! I had no problem with the PC before this and the CPU always lists as a dual core 6000+ (3ghz x 2) whatever I do. The system is stable and I have had no crashes throughout all this but less than 500Mhz for 800Mhz ram is simply not good enough considering it is only a few days old. Any ideas on what to do here? The Mobo is an ASrock ALiveNF7G-HDready and the memory is OCZ2G8004GK. They should be compatible and the Mobo does support 800Mhz RAM. I read that there were some problems with the multiplier for the 6000 and DDR6400 but I am not sure that is the problem here. All and any help gratefully received. Cheers

Look at the chart below to understand the difference between memory bus clock and I/O bus clock. http://en.wikipedia.org/wiki/DDR2_S...

Thanks OtheHill, but I am no wiser..(sorry, long day at work ;-() CPU-z reports a Dram Frequency of 249 mhz which I believe to be the single rate so it is actually just under 500 mhz but it should be running at 800. I have everything in the BIOS set back to auto as I only got 199mhz with manual settings. In CPU-Z my FSB:DRAM is listed as CPU/12 and the timings are at 4-4-4-12 while mine should be at 5-5-5-18. Sorry if I sound stupid but everything has been straight forward with this PC up to this-never needed to tweak anything in the BIO; stuff just ran as it should. I do not overclock and I wanted the extra RAM for heavy duty CAD/Vray rendering...I just don't know what else to try. Is it worth trying to manually set the memory to 667 in BIOS and just be happy with that speed?

Christ, that was weird...turns out Cool n Quiet was the culprit. I turned it off, set DRAM to 800 and now CPU-Z states 374.1 MHZ (so nearly 750 there!). My FSB:DRAM now reads CPU/8 which would be better at CPU/ 7 but then I guess that would be running at 860! Only problem now is the CAS timing which are 6-6-6-18 rather than the stated 5-5-5-18. Is it worth setting these manually or just be happy with this?

Are you running the DDR2 6400 modules with the DDR2 4200 modules? If so, the memory bus will run at the lower rated speed of memory module. You can verify by removing the lower rated modules and see if the speed comes up. Crucial shows compatible chips for the mobo.

"DDR2 6400 running at only 400Mhz!" PC2-6400 (aka DDR2-800) is supposed to run at 400MHz. 800MHz is the "effective" speed due to double pumping. 400MHz frequency is what you should be looking for...or as close to it as possible. The memory divider has to be a whole number, so with your CPU clocked at it's default settings, you will never get your RAM to run at exactly 400MHz. The best you will be able to do is 375MHz unless you change your CPU clock settings. For example, right now, your FSB:DRAM ratio is listed as CPU/12...in other words, 3000/12 = 250MHz. If the divder was 7.5, the RAM would run at 400MHz but since the 7.5 divisor is not possible, it would have to be 3000/8 = 375MHz. "I have everything in the BIOS set back to auto" That's a big part of your problem. The BIOS should ALWAYS be manually configured. BIOS defaults are NEVER 100% correct. Have a look at these settings to get a general idea of how it should be setup: http://www.pcstats.com/articleview....

Hey, looks like you figured it out while I was typing away! "Is it worth setting these manually or just be happy with this?" Yes, set them manually.