My motherboard has 4 memory slots and 2 are populated with PC6400 DDR2 400mhz 2gb(ea) dimm's.
The motherboard says the maximum supported memory clock is 400mhz.
Will 2gb 800mhz PC6400 DDR2 dimm's work at all, and if so will they work in the 2 empty slots if I leave the original dimm's in place (to give me a total of 8gb of ram)?
Thank you in advance!
Update:*it's PC2 6400 not PC6400 if it makes a difference.
Verified answer
Those will work fine.
The actual base speed of PC2 6400 DDR2 RAM is 400Mhz. The "effective" speed of 800Mhz (the one that's advertised) come from multiplying the base speed by 2. It's Double Data Rate memory, so it's read twice per clock cycle.
While it's always best to match your existing modules, faster RAM usually works too. Newer RAM modules have SPD ratings for lower frequencies as well. Many motherboards automatically downclock higher-rated RAM to a usable speed, the rating is just the *maximum* frequency at which it can operate.
It's going the other way that doesn't work... A motherboard that recognizes PC2 6400/8500 RAM wouldn't take PC2 4200 memory because those modules aren't fast enough.
Anyway, in this case there's no problem. PC2 6400 is PC2 6400.
Stay away from any modules with a higher frequency supported by your motherboard. Assuming your motherboard and operating system support more memory utilization, stick with the same module types as you are currently using.
no don't do it. it will crash your pc.