what's the truth behind the ddr400 memory compatibility?

Discussion in 'Asus' started by Vin, Jun 14, 2005.

  1. Vin

    Vin Guest

    Why do some mobos full support (or nearly full) the ddr333 and not the
    ddr400?

    Vini
     
    Vin, Jun 14, 2005
    #1
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  2. Vin

    Ed Guest

    Probably because the chipset on the board is older and wasn't made to
    support DDR400 when it was released.

    Ed
     
    Ed, Jun 14, 2005
    #2
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  3. Vin

    DaveW Guest

    They use older chipsets that did not support DDR 400 when they were
    introduced.
     
    DaveW, Jun 15, 2005
    #3
  4. Vin

    Vin Guest

    ok, but what about the mobos of today? they actually do not support all the
    ddr400 memories! (i'm guessing for what i saw)

    Is it the ddr400 now full supported (like the ddr333) for any mother of
    asus?
     
    Vin, Jun 15, 2005
    #4
  5. Vin

    Paul Guest

    Electrically, it is pretty hard to drive memory at DDR400
    or higher (when multiple DIMMs are involved). If the only
    job a Northbridge had to do, was drive the memories, the
    design might be easier to achieve. The compromises come,
    when other circuitry and interfaces are added to the Northbridge.
    (For example, there are hardly any Northbridge chips with integrated
    graphics cores that work properly. The 865GE might be the only
    one of its generation. I haven't read too many reports about
    current generation integrated graphics chips, with regard to
    proper operation. ATI doesn't count, because their BIOS are
    so screwed up.)

    The same problems occur, even when the memory controller is
    placed inside the processor, as is done in the Athlon64
    family. They have problems driving DDR400 as well. (You have
    to set Command Rate to 2T, to get them to work.)

    In any case, the easiest driving task, is driving a single
    stick of memory on a memory channel. It especially helps if
    the DIMM is single sided (8 chips instead of 16 chips). None
    of the trends that allow high memory speed, allow lots of
    memory to be added to the computer.

    DDR DIMMs have been run higher than DDR600, but never in
    a four stick dual channel configuration. Similarly, don't
    expect a three slot single channel motherboard to run
    three sticks of memory at DDR400 rates.

    One notable exception is the Nforce2 chipset. When you use
    CAS2 DDR400 memory, you can run three sticks on there without
    a problem. The trick in that case, is there are three separate
    address busses (or so it is claimed) coming from the Nforce2
    Northbridge. Using separate busses, means the load on each
    interface is a single stick of RAM. That is why that load
    can be successfully driven.

    That kind of solution is seldom used on Northbridge chips.
    To keep the price of a chipset low, you cannot let the pin count
    on the bottom of the chip get too large. Basically, the price
    is determined by the pin count, and not by the silicon itself.
    That gives an incentive to not use multiple address/command
    busses.

    Intel has a development called FB or fully buffered memory. It
    is a new form factor DIMM, where the chips don't directly
    connect to the bus. Each DIMM has buffer chips, to decouple the
    memory chips from the bus. A point to point connection is used
    from the FB to the Northbridge. One advantage of this concept,
    is no new kinds of memory need to be created. The buffer chip
    must be custom designed for DDR and DDR2, so a different kind of
    memory needs a different kind of buffer chip. Because the interface
    is point to point from FB DIMM to Northbridge (the DIMMs do not
    share a bus), there should be no issues with such a product
    meeting its stated performance targets. As to when this will
    be introduced into a commercial product, only time will tell.

    http://www.theinquirer.net/?article=15167
    http://www.theinquirer.net/?article=15189
    http://www.theinquirer.net/?article=15214

    As long as the current generation of motherboards uses shared
    busses, where more than one electrical load is placed on the
    bus at a time, there will be problems with loading and
    compatibility. While this concept has kept the price of the
    motherboard lower, it has not made the customer experience
    a pleasant one.

    Some day, all interconnect on the motherboard will be point to
    point. The PCI bus was a shared bus, with many loads sitting
    on the same bus lines. PCI Express, the replacement, uses point
    to point unshared connections, from each PCI Express peripheral
    chip, to the bridge that drives the bus lines. Engineers will
    try to make all high speed interconnect that way, due to the
    ease of design. Look at disk drives - previously we had two
    drives sharing a ribbon cable, and now we have point to point
    SATA interconnect to the motherboard. The Northbridge and
    memory interfaces will be the last things to receive a
    redesign.

    Paul
     
    Paul, Jun 15, 2005
    #5
  6. Vin

    J&SB Guest

    Excellent explanation Paul. Thanks for the insights.
     
    J&SB, Sep 8, 2005
    #6
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