Ram speed compatibility

[cyn325]

Can ram of different speeds (say 400 & 800) be used in the same computer? I'm getting a new computer that comes with 800 spd modules (2). Other than the spd, the 2 modules in my old computer are the same type. My old ones are only 400's. There are supposed to be 4 slots on the new computer. What I am wondering is will the old modules be compatible & work in the new computer to increase my ram or would I need to buy new ram to put in it if I want to upgrade the amount of ram.

 

[cyn325]

Can ram of different speeds (say 400 & 800) be used in the same computer? I'm getting a new computer that comes with 800 spd modules (2). Other than the spd, the 2 modules in my old computer are the same type. My old ones are only 400's. There are supposed to be 4 slots on the new computer. What I am wondering is will the old modules be compatible & work in the new computer to increase my ram or would I need to buy new ram to put in it if I want to upgrade the amount of ram.

nvm, just noticed one is ddr & the other ddr2 so that probably rules out compatibility.