I have just put myself a pc together and every time i put the memmory to 1066 the system becomes unstable keeps crashing locks up and will not let me input anything have to reset the pc works fine in 800 but when you pay more for the speed you what to use it.

im running: AMD 9950 runnig at 2.61
ASUS CROSSHAIR FORMULA 2 780A
8GB OF GELL BLACK DRAGON PC8500 5.5.5.15.t2 is what it says on the ram.
X2 IN SLI ASUS EN8800GT 1GB

This motherboard is unstable running memory at this speed.

This is according to a review here ;-
InsideHW - ASUS Crosshair II Formula

Not every mobo is equal. It is always good to do a bit of investigation before you buy something. Look at reviews, rants and raves. You will always get someone that has had a problem with a product but if the general concensus is the mobo is good or bad then you know wether to buy it or not.

I'd try it with 4-4-4-12@800 and if that doesn't work go with 5-4-4-12@800, both at 2t, of course. Some mobos just have a rough time with 1066 in all 4 slots. Watch the voltage, too. Sometimes the mobos will set the voltage low. Usually 2.0 or 2.1 volts are required to hit 1066.

Originally Posted by swarfega

Ive managed to set it at 4-4-4-12-2t@800. Is the ram now running at full speed?

Pretty much. DDR 800 is the top JEDEC DDR2 speed. 1066RAM just has chips that are rated to overclock. If you run your RAM at 800, it should be rock solid. Running at 1066 is an overclock (even if they're sold as 1066) and usually requires a boost in voltage to attain. With the boost in voltage comes an exponential increase in heat, causing instability unless you address the heat. That and some mobo voltage regulators may 'burn out' at that increased voltage. The 800 at 4-4-4-12-2t should be just as fast as 1066 at 5-5-5-15-2t.

And 4 sticks are always more taxing on the memory subsystem than 2 sticks. Adding 2 sticks will almost always lower the Vista WEI score for RAM, since that score is based on throughput and Vista has to access more RAM to test it. Average throughput will usually be lower the longer the test is run.

Anytime.