DDR vs. DDR2

Would someone PLEASE explain to me the difference between the two technically? Is DDR2 Quad Data Rate or what?

That would be QDR. I think DDR2 is just higher clocked DDR, with higher latency.

Nope, QDR and DDR-II are quite different things, or at least, in theory. In practice they do much the same. I'm assuming you know how standard DDR memory works in all of this.

In brief, QDR (also known as dual DDR) uses identical two sticks of DDR which run on alternating clock cycles. To put that into English, imagine you have two sticks of 200 MHz RAM, running on a 400 MHz bus. It wouldn't take a genious to tell that therefore you would have only one piece of data going down the bus every two cycles. QDR therefore alternates between DIMMS, giving the illusion of a higher clock speed, even though the DIMMS themselves are running at the same speed as normal.

DDR-II works on a similar system, except on a lower level. Instead of using two alternating DIMMS to double the speed, they use banks within the modules themselves to do this. They are then regulated by a controller on the DIMM and sent down the bus. The benefit of this is that you can also send data at four times the clock rate of the chips except without needing two identical modules.

Because of these changes, it also means the packet lengths in both QDR and DDR-II increases from 2 to 4, due to the way that the illusion of speed is provided. Anyway, I've already gone way into the realms of what should be in technical discussion, so if you want to learn more, have a read of:

http://www.xbitlabs.com/mainboards/ddr-ii/

Well, what you first described is different from QDR. QDR is different from dual DDR. QDR simply sends 4 signals per clock cycle where dual DDR sends 2 signals per clock per channel.

So essentially what you're saying is that DDR2 IS QDR with a different name?

Voodoo Rufus said:

Well, what you first described is different from QDR. QDR is different from dual DDR. QDR simply sends 4 signals per clock cycle where dual DDR sends 2 signals per clock per channel.

So essentially what you're saying is that DDR2 IS QDR with a different name?

Click to expand...

confused the crap out of me too!

I just read the article. Interesting. Basicly, the clock rate of DDR2 chips is 1/2 that advertised but operating at QDR. Very nice.

So GFFX has 250MHz chips running at effective 1000MHz.

Thanks for the link...been out of the loop for a few months and needed the info on DDR II to get back on top of things.