Dual Channel DDR basics...

Discussion in 'Links' started by syntax_error, Feb 10, 2003.

  1. syntax_error

    syntax_error Make it So

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    With the new NForce, Granite Bay and SiS655 chipsets now available we now have this thing called Dual Channel DDR.

    Here is a 'general idea' behind Dual Channel DDR as it relates to the P4. (works fairly well for AMD as well...just adjust the CPU FSB value)

    The difference in single channel operation and dual channel operation is in the way the motherboard uses the memory...nothing to do with the memory modules itself. For DCDDR to work you need to have two modules of memory, ideally the same size and specifications for optimum compatability.

    Dual channelling has been done for some time already...it's the way almost every 16bit RDRAM P4 setup runs...Dual Channel... you need to have your memory run in pairs. Interestingly enough RDRAM now has a 32bit Single Channel version available (though not widely adopted).

    Imagine your mobo is like a factory. There is the CPU on one side and the Memory on the other side. Both areas work at certain speeds. Both areas have data for the other to work on. Each area has a door that is a certain width to allow data to come and go and a rate at which the work can enter/leave.

    The CPU operates at 533mhz (fsb) and has an access door that is 8bytes (64bits...there are 8bits in one byte) wide. 533mhz x8 bytes = 4264mb/s. This is the theoretical amound of data that can pass through to the CPU per second.

    In Single Channel DDR operation all the memory is in one room and there is only one access door or one channel that is 8bytes (64bits) wide. Let's say the memory is set at 333mhz. 333mhz x 8 bytes = 2664mb/s. This is the theoretical amount of data that can pass through the memory per second. This rate is lower than what the CPU can potentially put out, therefore the CPU waits for the memory.

    In Dual Channel DDR operation it's like the memory is in two separate rooms with two access doors or 2 channels, each 8bytes wide (16bytes or 128bits total). The memory is at 333mhz. 333mhz x 8bytes x 2= 5328mb/s. This is the theoretical amount of data that can pass through the memory per second. Double that of what was available in single channel operation. The CPU isn't waiting any more.

    Granite Bay uses a default DDR266 in dual channel. 266x8x2= 4256mb/s ...almost matching the 533fsb CPU's bandwidth perfectly. As the P4 moves up to an 800mhz FSB, DDR400 will become the matching memory for this CPU.

    Don't expect miracles with all of this increased memory bandwidth though...it does improve overall performance as there aren't parts waiting around for each other, but that increase in performance doesn't fully reflect the 'doubling' of available bandwidth. There are other forces at work too...latencies, timings, inefficiencies etc. Consider that current single Channel DDR333 and 400 setups can run within 5-10% of RDRAM and DCDDR setups despite their memory bandwidth disadvantage. Various applications will benefit more/less than others for each setup.

    I see the main advantage of Dual Channel operation is that it relaxes the need for running DDR at very high speeds.
     
    Last edited: Feb 10, 2003
  2. mikeap

    mikeap Active Member

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    syntax-error,

    Great post! I'm almost figuring it out!! It's really starting to make sense! Please post more of these.
    In researching what components to purchase for a new system, I'm finding it a challenge to procure the correct ones as to not create a bottleneck. I also want to have some "room" for a later upgrade. I'm pretty much set on a P4, but have not been able to settle on what platform I want to go with as far as a mobo is concerned. The biggest questions being DDRam or RDRam, and a board that supports 8X AGP.

    Articles like yours are helping to clear the fog...

    Mike
     
  3. soopersonic

    soopersonic Ancient Guru

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    HI syntax!
    Great post but one more question:
    Do dual channel DDR mobos only run with two memory modules?

    soopersonic
     
  4. syntax_error

    syntax_error Make it So

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    Running regular DDR mode is also available.
    How you arrange then into the slots determines how it's going to run...consult manuals of specific motherboards for it's memory arrangement options.
     

  5. soopersonic

    soopersonic Ancient Guru

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    Does the Gigabyte 8IEXP support dual channel DDR? Probably not right? Well didn't anything see about it at least...

    thanks again

    soopersonic
     
  6. PixelDude

    PixelDude Pixelated Guru

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    Note that you need the same size and type of Memory DIMMs, preferably having the same CAS Latency rating and chip manufacturer to increase stability.

    Corsair sell pairs of DIMMs called "TwinX memory kits" that have been tested in a dual channel arrangment and guarantee to work at the labeled speed. The 2-2-2-5 versions are also excellent for overclockers who push their CPU to run above the default 533FSB of late C1 Pentium 4's (sometimes up to around 700MHz). Here is the link.
     
  7. JACK4HIRE

    JACK4HIRE Ancient Guru

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    Just bought a Gigabyte GA-8INXP and let me tell you guys at 166 Mhz FSB this thing screams. There is definately a noticible speed diffrence between this board and my Abit IT7-Max 2.
     
  8. Coolppl

    Coolppl Master Guru

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    Yes! This tells me my P4S8X can still kick somewhat ass!
     
  9. Lofoscopico

    Lofoscopico Member

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    are there any boards, with dual-ddr 333mhz support?
     
  10. soopersonic

    soopersonic Ancient Guru

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    yeah check asus' website for boards like that. There are dual 400MHz boards as well.
     

  11. L10nH34Rt

    L10nH34Rt Master Guru

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    Re: Re: Dual Channel DDR basics...

    Hm.. don't think so :rolleyes:
    Your mobo is based on SiS 648 which doesn't use Dual-DDR.
    Sorry :(
     
  12. Kyaner

    Kyaner Hellenic Guru

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    Question : the Abit IC7-G which i will have hopefully soon supports dual channel ddr mode on a single chip and i am planning on combaning the board with a single 512mb chipset from Corsair.

    So will i c any real performance gain from setting the board to use the single chip in dual channel ? I do understand the way dual channel mode works for 2 chipsets but has anyone tried it on a single ?

    Taken from Abit's FAQ

    Q: Does ABIT IC7 series mainboard support DDR266, DDR333, and DDR400 in single and dual channels? ( IC7-G / IC7 )

    A: ABIT IC7 series mainboards do support dual channel DDR 266/333/400. With only one DDR memory module installed (single channel mode) the board still works fine but we highly recommend users install memory modules in pairs to feature the best performance by dual channel mode.

    Their asnwer is not detailed enough for me, that's why i made this post :)

    Thanx in advance :)
     
  13. soopersonic

    soopersonic Ancient Guru

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    That answer clearly states that you will use Single Channel mode with only one stick of RAM installed. There's no way to use Dual Channel without two sticks of RAM
     
  14. Kyaner

    Kyaner Hellenic Guru

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    Question retracted, it's official i am an idiot :D
    Or i was too sleepy when i posted...
    In any case, sorry about that
     
  15. lmao kyaner,

    thnx alot syntax, i was troubled with dual ddr and you enlightened me, i bow in respect to you since you tought me something, and i respect teachers(not talking bout everyday school teachers), i had a long conversation about fsb with my cuz he seemed to retreat and said he was talking bout sumtin else, i told him that your total ram bandwith cannot passyour cpu bandwith because then it would not work but he refused, im right right? like 800 mhz p4 is 6400 and dual ddr 400 2x4000 800 800x8 6400
     

  16. ortuno2k

    ortuno2k Guest

    very helpful.
    thanks.
     
  17. fallenx

    fallenx Ancient Guru

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    Dual Channel works by having the same amount of memory per memory channel. So it is possible to run dual channel without using 2 sticks of ram. For example, a 1024mb ram configuration can be run the following ways.

    1x512mb 1x512mb
    2x256mb 2x256mb
    1x512mb 2x256mb
     
  18. Martys Web

    Martys Web Don Santino Corleone

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    If your going to do this make sure you buy the memory kits that are rated for Dual chanel. You will only pay a few dollars more and your system will be stable.

    Most all the big boys like OCZ/Corsair ect now sell it that way.
     
  19. CVND

    CVND Master Guru

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    so youre telling that a 512mb ddram is same fast as a 1024mb of sdram?
     
  20. BLyarx

    BLyarx Ancient Guru

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    He is saying running ram in dual channel is faster then single channel ddr ram .. If you have a 128x2Mb stick running in dual channel it will run faster then a 1024Mb's of single channel ddr.

    And no SDRAM is not as fast DDRAM.

    Ram size and speed are two different things.
     

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