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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  • 13Gigatons - Wednesday, May 16, 2007 - link

    Suddenly it doesn't seem like a bad decision on AMD's part to hold off on their move to AM3 and DDR3 until 2008/2009. I really don't get why we need to change the memory technology so fast, with DDR2 finally dropping in price so fast.

    I'd rather have 4GB of DDR2 then 1GB of DDR3.
    Reply
  • Sunrise089 - Wednesday, May 16, 2007 - link

    Actually, a 2%-5% performance jump is very impressive from anything other than a CPU or GPU. Running a Raptor versus a 7200RPM drive, or a high-end motherboard versus a budget model, or a add-on sound card versus onboard audio all are choices many people make without any huge double digit performance gains in most applications.

    Thats said, the 2%-5% gain isn't from the memory standard (did you even read the article?) but from the new chipset. So these numbers have absolutely no bearing on AMD's choices.
    Reply
  • Googer - Tuesday, May 15, 2007 - link

    If you wanted to test bandwidth effects, why use a processor that is not very bandwidth dependant? Instead a bandwidth hungry LGA-775 Prescott should have been one the CPU's used in these DDR3 benchmarks. I'd like to see this article updated with a dual core netburst processor added. Reply
  • TA152H - Wednesday, May 16, 2007 - link

    Are Prescotts even relevant anymore though? I mean, how many people are going to be perspecacious enough to buy a P35 based motherboard, and care about memory performance, and then go out and buy something as foul as a Prescott? It might make for an interesting data point, but it's a very little practical value. Reply
  • vailr - Tuesday, May 15, 2007 - link

    Please include, in your forthcoming P35 board review: enabling SATA AHCI mode. Still remains puzzling, especially when a board uses a non-Raid Intel chipset, such as the ICH8. Gigabyte says on their web site, that on the GAS-965P-DS3, that AHCI should only be enabled when running Vista. Several other questions remain, such as: AHCI seems to work fine under WinXP when using the latest 1.17.17 JMicron drivers (single HD connected to a JMicron SATA port). Connecting the same HD to an Intel port, and AHCI won't work. Intel's offical AHCI drivers only seem to install when a Raid array is present.
    In summary: please include comments on any differences and/or improvements in AHCI support between the 965 v. P35 chipsets.
    Reply
  • Comdrpopnfresh - Tuesday, May 15, 2007 - link

    There was an article a few months ago saying that speed increases on ddr2 didn't really matter, the architecture for the memory was old enough that there was a decline in performance advantage as speeds increase. If ddr3 is basically the same as ddr2, wouldn't the same be expected? Does anyone have any idea when the timings will come down? The voltage is nothing to gawk at- it's the reason for the increased speed. On the gate level, the less space between high and low, he faster a gate can transition. I'm most interested to see ddr3 performance and bandwidth numbers w/ amd processors. Reply
  • R3MF - Tuesday, May 15, 2007 - link

    i currently have
    an X2 system with PC3200 dual channel
    and a C2D system with PC6400 dual channel

    i definitely see a quad core 3.2GHz chip running PC12800 in my future.

    hooray for technology!
    Reply
  • DeepThought86 - Tuesday, May 15, 2007 - link

    I wonder how long before Intel gets impatient and starts not-so-gently shoving DDR3 down people's throats long before the price or performance justify it?

    "Oh look, our chipsets for Nehalem don't support DDR2, woops you'll have to dump your DDR2 and get this spiffy new stuff. Look, it went from 2 to 3, it must be better!"
    Reply
  • theprodigalrebel - Wednesday, May 16, 2007 - link

    I remember reading an article somewhere where the interviewer asked an AMD person about Intel pushing for DDR3. The guy admitted that DDR3 is the way of the future - though not ready/relevant today - and only a company like Intel can drive that change.

    In his words, AMD's move to DDR2 came at the right time - in terms of price and advances in bandwidth/latency where DDR2 finally defeated the best DDR kits. He admitted that the move wouldn't have been possible unless Intel had moved the market in that direction over the past year or so.

    Intel has driven changes from AGP to PCI-Express, IDE to SATA and DDR to DDR2. It seems forced at first - and it probably is - but you don't HAVE to be an early adopter. You had the 925 chipset introducing DDR2 and 915 boards supporting DDR. That is exactly what is happening here.
    Reply
  • TA152H - Tuesday, May 15, 2007 - link

    You need for Intel to push stuff down people's throats, or you'd never get these changes. No other company is in a position to, it's like IBM used to be almost 20 years ago.

    The price of the memory will go down as production goes up, which of course is driven by demand, which of course has to be driven by Intel. If not Intel, then who?

    By offering a chipset that offers both, they are slowly starting the transition and the prices should get closer. At some point, supporting DDR2 is just a waste of chipset space and is costing people money that have no intention of ever using it, so you get rid of it. At that point it might cost a little more still, but that's the price you pay for transitioning to a better technology, and making that technology cost effective. I think they're extremely important to the industry for exactly that reason, not a malicious force.
    Reply

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