My PC is DELL PRECISION 390
Mother Board Dell 975X with 2 GB RAM
MY PC comes with DDR 2 667 Mhz 2 RAM Cards
I just inserted 800 Mhz 1GB RAM with these 667 Mhz 2GB RAMs (now 3GB)
My System working fine without any issue..
but is there any problem by using different frequency rate RAM cards ??
Your machine has 4 DIMNs supporting upto 8 gb DDR2 533/677......However it means that the 800 mhz RAM you bought would be operational on 667 mhz only. The PC would always operate the ram at a common frequency (both at which the other rams are and the max it can handle).But anyways you don't have to worry.You will be able to use the full 3 gb RAM at 667 mhz.