Hi There ...    
 
I wanna know wether if I can use my 4 gigs G.skill RAM at 1066 on a motherboard ( XFX 650i Ultra) whichi supports up to 800 ?  
 
Thx in advance  

I'm 99% sure it will work. All DDR2 RAM will scale back down to the maximum speed the mother board allows it to operate at. For example DDR2-667 will run in a motherboard who's max supported speed is DDR2-533. Although I don't understand why you'd want 1066, this being the case. Extreme overclocking? If it only supports up to 800 and you don't overclock, you'll be paying extra for nothing.

well ... i bought it cuz it was available !!! :-o
 
... one more thing ... the ram's specific model is : G.SKILL F2-8000CL5D
 
it's been writen on the cage that the bus is : 1000 ( not 1066 )
 
and of course the sugessted voltage is 2.0 ~ 2.1 which i think is compliely supported by 650i mainboards ...
 
any idea ?

Well if it's written PC2-8000, then it's a DDR2-1000.  
 
I think it will run on your mobo @800MHz. But if you plan to run it at 1000MHz then I'm quiet pessimistic. Some people found problem at n6xx series running more than 800, though some others did prevail ..  
 
Don't really need for 1000 IMO, if you have 800 already, then don't waste your money on it.

yeah ... I know ... as a matter of fact there is no noticeable difference ( especialy in gaming ) between 800 and 1000 ...
 
I just wanted to know if I am going to have an unmatching issue or not .
 
It seems that i won't  
 
cheers then !

The JEDEC specification for DDR2 is 533, 667, or 800 @ 1.8v.  All memory sold as DDR2 is required to run at one of these settings and will have settings for one of those speeds on the SPD chip.  Most highend RAM sold currently is sold at it's overclocked or EPP settings which is just a guarantee by the manufacturer that the memory will be stable at those speeds.

To give you an example this is from my RAM which is sold as DDR2 800 4-4-3-10 @ 2.1v

The actual JEDEC specification is 5-5-5-15 @ 1.8v but it was sold at it's overclocked rating.

Edit: Typo

Yes, it should work. Never kew of anyone who had problems running memory at SLOWER than spec speeds.