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DDR vs. DDR2

42780 Views 11 Replies 6 Participants Last post by  dai
Hello all. I am wondering if someone can point me in the direction on where I could read more about DDR vs. DDR2. I have DDR 400MHz RAM now but I am awaiting a rig in the mail that's going to have 667MHz DDR2 RAM I am wondering how much of a difference there will be? The problem is I wont be able to compare the RAM between the two rigs because the speeds of RAM will be different plus it's going to be a differnet CPU/graphics card combo. Simply put is DDR2 that much better then DDR and where can I read about the specific advantages? Thanks. :grin:
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DDR400 does not perform better than DDR2400; thats well known. AMD stated this before making DDR2 slots mainstream. However, above that DDR2 performs better, especially with DDR2800.

DDR versus DDR2 on i915 - Benchmark - PCmark2004

From AMD (an old link not available now):
What is DDR2?

“Double Data Rate, Two” or simply, DDR2, is an extension of a system's standard DDR memory. Like DDR, DDR2 transfers data on both edges of the system clock, which allows the bandwidth of the memory to equal twice that of Single Data Rate memory, or SDRAM. DDR2's architecture is intended to increase efficiency and performance over its predecessor, DDR.

What are some of the major differences between DDR and DDR2?

One of the main differences between DDR and DDR2 memory is the required voltage at which the memory runs. DDR's standard voltage setting is 2.5 V, while DDR2's voltage setting is 1.8 V. Although it may not be a phenomenal difference, the lower voltage specification allows more space for operation at higher frequencies.

A second difference between DDR and DDR2 memory is DDR2's 4-bit data pre-fetch. DDR has two sets of data that are read and written to the memory core, while DDR2 allows for four sets of data to be processed. DDR2's internal data bus is doubled, which increases the die size. Although the die size is increased, the memory core internally operates at half the frequency. This allows DDR2 to run at the same frequency of DDR, but at twice the speed. For instance, DDR2 memory at 400MHz runs at the same frequency as DDR memory running at 200MHz.

A third difference is the write latency of DDR2. DDR's write latency is one clock. This allows for data to be written to the memory one clock after the write command has been issued. With DDR2, the write latency becomes two clocks. The doubled clock cycle allows for twice the data to be written to the memory after the write command has been issued.

A fourth difference is DDR2's new feature called On-Die Termination (ODT). ODT permits the user to terminate signals in the memory itself. The termination of DDR is done on the motherboard. ODT drastically reduces signal wave reflections from the termination network and promotes enhanced systems margins. ODT permits fewer capacitors and resistors on the motherboard, which helps reduce cost and makes memory subsystem layouts to be more efficient.

Why use DDR2?

There are several reasons why DDR2 should be considered. First, the required voltage is lower and reduces the system power demanded by the memory. Second, the increased pre-fetch produces a reduced core speed dependency for better yields. Third, DDR2 allows migration of higher bus speeds. Fourth, its write latency provides an improvement in command bus frequency. Finally, DDR2 provides additional features that improve the overall performance and effectiveness of the memory.

So why isn't everyone using DDR2?

DDR2's performance gains are not evident until you get to DDR2-533. In fact, it is not until you get to DDR2-667 where you begin to see measurable performance gains. This is due to the increase in latency that offsets any speed advantage until 667MHz. For the sake of comparison, DDR-400 outperforms DDR2-400 and runs comparable to DDR2-533.

DDR2 also costs significantly more than DDR. Since the 110nm fabrication process is far from standard, the cost of the DDR2 DIMMS is much higher and quantities are much more limited.

The true benefit of DDR2 is in its ability to achieve faster speeds with its lower voltage requirement. Eventually, DDR2 will make its presence felt in the marketplace, but it will be some time before the performance gains are truly realized.

To learn more about DDR2 and its specifications, AMD recommends contacting memory vendors who have developed or are developing DDR2 memory.
Thanks for the links! That's great info. Kalim did you mean to say that "DDR (400) DOES perform better than DDR2 (400)? Because according to this article the performance gains are not really evident until 533+ MHz and that DDR (400) outperforms DDR2 (400) because the increase in latency offsets the performance advantage. Then when getting to 667 and 800 MHz the performance gains become noticeable with DDR2 and it's a superior RAM at those speeds. Is that correct? If so I know HP is putting DDR2 (400) in some of the Pavilions now. Why would they put more expensive RAM in there if the performance gains aren't noticeable? Is there just an industry trend toward DDR2 now?
DDR400 performs better than DDR2400 yes. My mistake there. Above that DDR2 starts doing better. DDR3 is nearing the finish product now, so yes, they'll be gearing towards DDR2 mainstream acceptance.
Awesome info Kalim, thanks a lot. Happy Holidays.
You're very welcome. Enjoy your holidays too!
now i'm using intel motherboard D945PLRN and 512MB [email protected] RAM. i want to ask whether my motherboard can support [email protected]?
now i'm using intel motherboard D945PLRN and 512MB [email protected] RAM. i want to ask whether my motherboard can support [email protected]?
Afraid not.
It only supports DDR2-533 and DDR2-400.
Right now, no processors can benefit from DDR2 memory faster than DDR2-667 MHz. Only the Intel Xeon with a 1333 MHz FSB can benefit from the 667 MHz RAM in a dual channel pair, and the Core 2 Duo can't benefit from RAM faster than 533 MHz in a dual channel pair. The same goes for AMD AM2 processors.

Because of the limits of the FSB bandwidth, the only benefit of DDR2-800 MHz RAM is for overclocking and for video cards that use the system RAM as shared RAM.

Just some food for thought.
Can you run a DDR2 or DDR3 etc graphics card with DDR ram?
yes they run independently of one another
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