The main difference between DDR2 and DDR3 is that DDR3 can read out 2^3 times per reference clock, while DDR2 can only read out 2^2 times, the caveat being that it takes twice as many Ram cycles to respond to a request, as would a similar reference clocked DDR2 module. It can be faster, but only under specific conditions.
All of the DDR rams use the same raw ram chips as the original SDRAM, with the difference being in how many times per cycle the output interface can unload data, so, as long as you are accessing different parts of the RAM are being accessed, and the system knows enough in advance what it needs to access, you can get a major speed boost. On the other hand, if you're trying to access the same data over and over again, you don't get and benefit at all.
Think of it like commanding a rocket artillery group. All of the rocket launchers can fire off all of their rockets at once, and then they take a while to reload. That's the way the ram chips operate.
Now imagine that you have one phone, so you can only call one launcher at a time. How fast your group can shell things is going to be limited by how fast you can pick up the phone, relay the order, and they can respond to it. That's like the original SDRAM interface, which can only pull one bit per pin per reference clock cycle.
Now imagine you have eight phone operators. This means you can call eight batteries at once, and all of them can fire at the same time. As long as you have more than a few launchers, this will really increase you effective rate of fire, even though your launchers still respond, and still fire at the same rate, simply because you can keep more of them tasked. But, if you call the same eight launchers every time, you're going to be limited by how fast they can respond, reload, and all that. That is what DDR3 is like.
Harry Voyager
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