DDR2/DDR3 - Newb question?

[rapsux321]

I currently run with a gig of DDR2 800 and am looking to possibly upgrade since prices are so low. The problem is I plan on building a new Phenom system, with a decent DX10 card in about a year. I know Am2 boards are forward compatible to Am3, so I'm wondering if DDR2 would also still work with an AM3 processor (even if it slows it down). I'm only asking such a question because I noticed that both DDR2 and 3 are 240 pin sticks, I also realize that AM2 didn't scale as expected with memory speed increase, so if I could save some money by using DDR2 with a new system and sacrifice a bit of performance....

 

[chookman]

For starters... it sounds like you think you can put a DDR2 stick in a DDR3 dimm... this is NOT true, the notch is in a different position. So the only way for the new Phenom to support DDR2 is if the chipset is made to support it. Which i am not sure on...

 

[rapsux321]

So, wouldn't it make sense for DDR2 to work with AM3 because its the same motherboard that is forward compatible? Otherwise why would AMD say its forward compatible if in reality you would need to buy a new mobo for DDR3?

 

[Newf]

With AMD, the memory type depends on the processor. Intel for now is not that way. The AMD cpu you buy will determine which (DDR2 or DDR3) memory you will need. If your motherboard will support a Phenom chip, then so will its memory. Remember that the memory controller for AMD is on the cpu itself. Historically, AMD has NOT been willing to spend the die space to support more than one memory type per cpu design. Intel is free of this problem since it's the Northbridge that contains the memory controller (both an advantage and a curse).

 

[chookman]

Oops my bad Newf is right... forgot we were talking about AMD hehe... AMD CPU will determine memory type to be used. Intel use northbridge ATM but this will change with Nehalem as it will have memory controller on CPU like AMD do now

 

[exodus d63]

Okay, here is my question.
Let's say I have an AM2/AM2+ mobo with an AM3 Phenom in it.

The mobo's memory standard is DDR2 1200.

Now, can I put DDR3 sticks in the memory slots or do I have to stick with DDR2?