Question With Upgrading RAM

Currently I have 256MB of PC2100 DDR RAM, and I've been thinking of upgrading my Computer to another 512MB of DDR RAM, (for total of 768MB RAM) as I am in need of more power. But my question is that, are there any RAM-clock speed limitations? Does is matter what kind of clock speed the RAM chip has that I purchase? Say I buy 512MB PC2700 DDR RAM, to put alongside my current 256MB PC2100 DDR Ram, would they work well togther? Or would I have to buy RAM whose clock speeds support/match the motherboard,CPU,FSB and the current RAM chip? Also if I sell 256MB of PC2100 DDR RAM, how much money could I sell it for? Thanks

My System specs are as follows:

Cpu: AMD Athlon XP 2000+ @ 1.67GHZ (266MHZ FSB)
Motherboard: ECS K7S5A
Current RAM: 256MB PC2100 DDR RAM

 

When running two different speeds of ram, they will only run at the slowest speeds of the two.
Sometimes two different chips will have compatibility issues, can happen with different brand as well as chips with different speeds.
As far as ram clock speeds depends on the the speed that the ram will support & the speed's your PC/MOBO will support, there all different.
It would be pointless to install ram that support higher FSB than your mobo.

What your current ram worth? what brand & what timmings does it support?
I'm looking for a stick of pc2100 256mb, I could make an offer, PM me with spec's.

 

ok thanks for the info man, when I think of selling the RAM, ill let you know, I'm guessing its proabably worth 30-40 bucks