What is DDR3?

To provide compatibility and interchangeability for computer memory, the structure and form factor are controlled by a standards organization known as JEDEC. JEDEC specifies voltages, speeds, timings, communication protocols, bank addressing, and many other factors in the design and development of memory DIMMs. Taking a closer look at publications at www.jedec.org can provide insight into what DDR3 brings to the market and where it might go. Comparing DDR2 and DDR3 several interesting points stand out.

Official JEDEC Specifications
  DDR2 DDR3
Rated Speed 400-800 Mbps 800-1600 Mbps
Vdd/Vddq 1.8V +/- 0.1V 1.5V +/- 0.075V
Internal Banks 4 8
Termination Limited All DQ signals
Topology Conventional T Fly-by
Driver Control OCD Calibration Self Calibration with ZQ
Thermal Sensor No Yes (Optional)

Please keep in mind that JEDEC specs are official. They are a starting point for enthusiast memory companies. However, since there was never a JEDEC standard for memory faster than DDR-400 then DDR memory running at faster speeds is really overclocked DDR-400. Similarly DDR2 memory faster than DDR2-800 is actually overclocked DDR2-800 since there is currently no official JEDEC spec for DDR2-1066.

DDR speeds ran to DDR-400, DDR2 has official specs from 400 to 800, and DDR3 will extend this from 800 to 1600 based on the current JEDEC specification. Initial DDR3 offerings will be 1066 and 1333 will quickly follow. The 1333 speed is important because it matches the 1333 bus speed of the new Intel processors. The 1333 processors can run any speed of DDR3 or DDR2 memory, but 800 and 1067 will be overlap speeds with DDR2. 1333 will be the first DDR3 speed to offer enhanced memory speeds to current and future processors.

Since DDR3 is designed to run at higher memory speeds the signal integrity of the memory module is now more important. DDR3 uses something called "fly-by" technology instead of the "T branches" seen on DDR2 modules. This means the address and control lines are a single path chaining from one DRAM to another, where DDR2 uses a T topology that branches on DDR2 modules. "Fly-by" takes away the mechanical line balancing and uses automatic signal time delay generated by the controller fixed at the memory system training. Each DDR3 DRAM chip has an automatic leveling circuit for calibration and to memorize the calibration data.

DDR3 also uses more internal banks - 8 instead of the 4 used by DDR2 - to further speed up the system. More internal banks allow advance prefetch to reduce access latency. This should become more apparent as the size of the DRAM increases in the future.

DDR3 further reduces the memory voltage. In the past few years we have moved from 2.5V with DDR to 1.8V with DDR2. DDR3 drops memory voltage to 1.5V, which is a 16% reduction from DDR2. There are also additional built-in power conservation features with DDR3 like partial refresh. This could be particularly important in mobile applications where battery power will no longer be needed just to refresh a portion of the DRAM not in active use. There is also a specification for an optional thermal sensor that could allow mobile engineers to save further power by providing minimum refresh cycles when the system is not in high performance mode.

There is even more to DDR3, but for most enthusiasts looking at a new desktop system DDR3 can provide higher official speeds, up to 1600MHz. The higher speeds are available at lower voltage, with 1.5V as the official specification. There are many features that will not make much difference in DDR3 performance until we begin to see even faster and higher capacity memory. The question, then, is whether DDR3 memory provides better performance for the computer enthusiast than current DDR2?

Index DDR3 Memory and P35 motherboards
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  • vaystrem - Tuesday, May 15, 2007 - link

    Thank you for your response :) Reply
  • cool - Tuesday, May 15, 2007 - link

    What am I missing? How can you have DDR2 800 results for the DDR3 Bearlake mobo?
    Look at the 3rd row, 4 column of the Sandra benchmarks results on page 5.
    Reply
  • TA152H - Tuesday, May 15, 2007 - link

    Their chart is a little bit off. It is how they did their best to speed normalize DDR2 and DDR3, so for the DDR2 column for the Bearlake it is DDR2 memory they tested, for the DDR3 version, it is DDR3 memory.

    It's probably the most useful thing in there, in my opinion. It shows you get extra speed even at the exact same timings, with memory using lower voltage. It's pretty impressive.
    Reply
  • cmdrdredd - Tuesday, May 15, 2007 - link

    not very impressive to me considering the prices you'll be paying. That's $300 difference between a good DDR2 kit and a DDR3 kit (probably not even high bin or binned at all). Reply
  • TA152H - Tuesday, May 15, 2007 - link

    Well, agreed, currently you're not getting much bang for the buck, but that's always the case when new memory comes out. Look at the price of RDRAM, it never got better :P.

    But, obviously, the prices today mean essentially nothing for the future of the technology, it's just representative of it being a very new technology right now. I'd expect it should be a tiny bit more expensive everything else being equal because some of the additions to it, but it should be insignificant. It's a much cleaner design, and you get some performance on top of it, so I think it's a good technology. I agree, for now, it's difficult to validate the price of it. It's not even like you could say that you're better off getting a DDR3 based design now so you can reuse the RAM. The latencies are so poor on the current stuff you'd probably be aghast at using it a year from now, and you'd probably be able to buy 1 GB of DDR2 today, and 1 GB of DDR3 in a year for less than 1 GB today. So, right now, I don't think it makes much sense to anyone.

    Good thing for Intel pushing it though. Anyone that dislikes them needs to recognize how important they are for moving technology forward even at their own cost. Sometimes they've failed though, such as with RDRAM and, so far, EPIC.
    Reply
  • Wesley Fink - Tuesday, May 15, 2007 - link

    DDR3 will run at DDR3-800 6-6-6-15 timings. We will add this to the DDR-800 5/6-6-6- line to clarify. The point was to run all 3 boards and the two memories at the exact same speed and timings. 800 was the only speed that allowed this. Reply
  • cool - Tuesday, May 15, 2007 - link

    Thanks for the explanation, Wesley.
    I was confused thinking the P5K3 was maybe one of those motherboards that can take 2 types of different RAM, namely DDR2 and DDR3. But that is not the case.
    Reply
  • TA152H - Tuesday, May 15, 2007 - link

    I see timings of 5/6-6-6-15 and such. What does 5/6 mean? The P965 is running at five and the others at six? Reply
  • Wesley Fink - Tuesday, May 15, 2007 - link

    We added this clarification to Page 4 - Memory Test Configuration:

    "While memory timings were matched to the same memory speed wherever possible, there were a few settings where the chipsets did not allow a direct comparison. DDR3-800 runs at 6-6-6-15 timings. The P965 has options to set 6-6-6-15 timings but the board would not boot under any settings or voltage we fed it at 6-6-6 timings. The closest timings that would work on the P965 at 800 speed were 5-6-6-15. The P5K DDR2 board, based on the P35 chipset, would allow setiing and running 6-6-6-15 timings. This is reflected in our charts with the line ID of 5/6-6-6- for timings. We also tested DDR2 at the fastest timings it could achieve with complete stability on both the P5B Deluxe and P5K Deluxe. This was 3-3-3-9 at DDR2-800 and 4-4-3-11 at DDR2-1066."
    Reply
  • TA152H - Tuesday, May 15, 2007 - link

    That's clear, I think that will remove any questions relating to the charts. Reply

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