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DDR high and low density?

Discussion in 'Overclocking' started by job, Jul 30, 2006.

  1. job

    job Guest

    job, Jul 30, 2006
    #1
    1. Advertising

  2. job

    Paul Guest

    In article <MY9zg.511832$>,
    "job" <> wrote:

    > What's this about?I see this on low end DDR.Both have 64x64.What's the deal?
    > I'm aware of this on PC 100 SDRAM but not DDR.
    > http://www.pcprogress.com/products.asp?orderid=43846721220905703306197&cat=2
    > 77&pg=4


    This is about more than density.

    Each generation of RAM starts with a base array size. The chip package
    pinouts are designed, so that several output data bus widths are
    supported, giving flexibility in how modules can be constructed.
    The same silicon die can be used to satisfy several different
    pinouts, simply by wire bonding choices when the memory IC is
    assembled.

    At the 512Megabit level, some chip types might be 16Mx16,
    32Mx8, 64Mx4. The "x16" and "x8" types are defined as
    acceptable by JEDEC, for making unbuffered modules. With the
    "x16" chips, four of those chips on one side of the module,
    makes a bank.

    With the "x8" type, it takes eight of those chips on the side
    of a module, to make a bank. Basically, it takes as many
    chips as is necessary to make a 64 bit grouping (as the
    bus interface on a DIMM is 64 bits wide).

    Now, x4 chips are legal to build, but they are typically
    used on registered DIMMs. JEDEC standards would allow
    registered DIMMs to be built with x4 chips. It takes sixteen
    chips, enough to fill both sides of the DIMM, to make a
    single bank that way. That places sixteen loads on the shared
    chip select signal for the bank, and for any other "global"
    control signals for the bank on the DIMM. The registered
    DIMM, via the register chip on the board, buffers the
    control signals, so the motherboard does not see sixteen
    loads on a bank that is on a registered DIMM. A registered
    DIMM makes it possible to overload the signals, since
    they are driven by the register chip on the DIMM itself.
    The motherboard never sees the overload, since the
    register chip sits between the motherboard and the
    sixteen chips.

    It seems that the x4 chips are cheaper to make. I don't
    have any figures to back that up, except to observe that
    the market is flooded with generic (unbranded) unbuffered
    DIMMs that use x4 chips. JEDEC doesn't want the modules to
    be built that way, so the companies who make them, don't
    put their name on them.

    The unbuffered modules with x4 chips do work (kinda) on a
    limited set of chipsets. Some adverts on the web, actually
    list the chipsets where the module might work. The question
    they don't answer, is whether filling all memory slots on
    the motherboard, with those products, would be successful
    or not. Mushkin used to have a section of their web site,
    where they tested various motherboards, and I think the
    result was, they found exactly _one_ motherboard that could
    be filled with those kinds of sticks.

    At the 512MB DIMM level, there seems to be no incentive
    to screw around. You are fairly safe buying 512MB DDR
    DIMMs, as they'll usually be made with (16) 32Mx8 chips.
    That is two banks or double sided DIMMs. I don't even know
    if anyone makes 64Mx4 chips or not, they just don't seem
    to be used to make "bad" 512MB modules.

    There are also single sided 512MB DIMMs, which are safe to
    use on a motherboard, as long as the motherboard claims
    to be able to use 1GB modules. Those DIMMs would use 64Mx8
    chips, and only have 8 chips total. I don't even know if
    I could find you an example of a module like this now, so
    they would be reasonably obscure.

    At the 1GB DIMM level, both 64Mx8 chips and 128Mx4 chips
    are in play. A company can shave $20 off the price, by using
    the 128Mx4 chips. But the trick is, the module will be
    unbranded, since the (small) company making the modules
    doesn't really want to get in trouble with JEDEC. And the
    memory companies cannot police this, since the (small)
    company could tell them that they are being used to make
    registered 1GB DIMMs.

    The modules with the 128Mx4 chips are a favorite on Ebay,
    and as a result, I would never buy a 1GB module off Ebay.

    As a consequence, when you are shopping for 1GB DIMMs, you
    have to check (somehow) how they are constructed. If the
    advert says "we use 64Mx8 chips", then you are safe. If
    the company admits they are 128Mx4 chips or if the company
    gives that weird list of "this module works with SIS648,
    Via xxx" type of list, then that is an admission of the
    use of 128Mx4 chips as well. You will notice that
    there are no Intel chipsets in the list of acceptable
    chipsets.

    So they can call them "high density" if they want, but
    in fact they are improperly constructed modules that
    should not have been offered for sale in the first
    place. If you cannot fill a motherboard with those
    modules and be guaranteed that they work, what good
    are they ?

    On the previous generation of SDRAM, it truly was
    a density issue. The modules were all legally
    constructed and broke no rules. The difference between
    low and high density chips, was the width of the
    multiplexed row and column addresses. A high density
    chip had one more address bit, than there were drivers
    on the Northbridge (of chipsets like 440BX). As a consequence,
    only half of a high density chip could be addressed by
    the Northbridge. A module with 8 chips would be half
    recognized, while a module with the "lower density" 16
    chips in two banks, would be fully recognized. That is
    why you had to be careful when buying 256MB SDRAM for
    440BX motherboards.

    Paul
    Paul, Jul 31, 2006
    #2
    1. Advertising

  3. job

    job Guest

    Cool.Great explanation.But,This 64x64 thing and 128x64.Same as 128x4? The
    link I proved seerms not to go where I thought.
    Anyway,the dont recommend these for Intel.I wouldn't buy them for anything
    anyway.I was just curious. Alot of people just look at price when buying,as
    do I,but I'd like to know a bit more about these things.Thanks Paul.
    "Paul" <> wrote in message
    news:nospam-3107061320360001@192.168.1.178...
    > In article <MY9zg.511832$>,
    > "job" <> wrote:
    >
    > > What's this about?I see this on low end DDR.Both have 64x64.What's the

    deal?
    > > I'm aware of this on PC 100 SDRAM but not DDR.
    > >

    http://www.pcprogress.com/products.asp?orderid=43846721220905703306197&cat=2
    > > 77&pg=4

    >
    > This is about more than density.
    >
    > Each generation of RAM starts with a base array size. The chip package
    > pinouts are designed, so that several output data bus widths are
    > supported, giving flexibility in how modules can be constructed.
    > The same silicon die can be used to satisfy several different
    > pinouts, simply by wire bonding choices when the memory IC is
    > assembled.
    >
    > At the 512Megabit level, some chip types might be 16Mx16,
    > 32Mx8, 64Mx4. The "x16" and "x8" types are defined as
    > acceptable by JEDEC, for making unbuffered modules. With the
    > "x16" chips, four of those chips on one side of the module,
    > makes a bank.
    >
    > With the "x8" type, it takes eight of those chips on the side
    > of a module, to make a bank. Basically, it takes as many
    > chips as is necessary to make a 64 bit grouping (as the
    > bus interface on a DIMM is 64 bits wide).
    >
    > Now, x4 chips are legal to build, but they are typically
    > used on registered DIMMs. JEDEC standards would allow
    > registered DIMMs to be built with x4 chips. It takes sixteen
    > chips, enough to fill both sides of the DIMM, to make a
    > single bank that way. That places sixteen loads on the shared
    > chip select signal for the bank, and for any other "global"
    > control signals for the bank on the DIMM. The registered
    > DIMM, via the register chip on the board, buffers the
    > control signals, so the motherboard does not see sixteen
    > loads on a bank that is on a registered DIMM. A registered
    > DIMM makes it possible to overload the signals, since
    > they are driven by the register chip on the DIMM itself.
    > The motherboard never sees the overload, since the
    > register chip sits between the motherboard and the
    > sixteen chips.
    >
    > It seems that the x4 chips are cheaper to make. I don't
    > have any figures to back that up, except to observe that
    > the market is flooded with generic (unbranded) unbuffered
    > DIMMs that use x4 chips. JEDEC doesn't want the modules to
    > be built that way, so the companies who make them, don't
    > put their name on them.
    >
    > The unbuffered modules with x4 chips do work (kinda) on a
    > limited set of chipsets. Some adverts on the web, actually
    > list the chipsets where the module might work. The question
    > they don't answer, is whether filling all memory slots on
    > the motherboard, with those products, would be successful
    > or not. Mushkin used to have a section of their web site,
    > where they tested various motherboards, and I think the
    > result was, they found exactly _one_ motherboard that could
    > be filled with those kinds of sticks.
    >
    > At the 512MB DIMM level, there seems to be no incentive
    > to screw around. You are fairly safe buying 512MB DDR
    > DIMMs, as they'll usually be made with (16) 32Mx8 chips.
    > That is two banks or double sided DIMMs. I don't even know
    > if anyone makes 64Mx4 chips or not, they just don't seem
    > to be used to make "bad" 512MB modules.
    >
    > There are also single sided 512MB DIMMs, which are safe to
    > use on a motherboard, as long as the motherboard claims
    > to be able to use 1GB modules. Those DIMMs would use 64Mx8
    > chips, and only have 8 chips total. I don't even know if
    > I could find you an example of a module like this now, so
    > they would be reasonably obscure.
    >
    > At the 1GB DIMM level, both 64Mx8 chips and 128Mx4 chips
    > are in play. A company can shave $20 off the price, by using
    > the 128Mx4 chips. But the trick is, the module will be
    > unbranded, since the (small) company making the modules
    > doesn't really want to get in trouble with JEDEC. And the
    > memory companies cannot police this, since the (small)
    > company could tell them that they are being used to make
    > registered 1GB DIMMs.
    >
    > The modules with the 128Mx4 chips are a favorite on Ebay,
    > and as a result, I would never buy a 1GB module off Ebay.
    >
    > As a consequence, when you are shopping for 1GB DIMMs, you
    > have to check (somehow) how they are constructed. If the
    > advert says "we use 64Mx8 chips", then you are safe. If
    > the company admits they are 128Mx4 chips or if the company
    > gives that weird list of "this module works with SIS648,
    > Via xxx" type of list, then that is an admission of the
    > use of 128Mx4 chips as well. You will notice that
    > there are no Intel chipsets in the list of acceptable
    > chipsets.
    >
    > So they can call them "high density" if they want, but
    > in fact they are improperly constructed modules that
    > should not have been offered for sale in the first
    > place. If you cannot fill a motherboard with those
    > modules and be guaranteed that they work, what good
    > are they ?
    >
    > On the previous generation of SDRAM, it truly was
    > a density issue. The modules were all legally
    > constructed and broke no rules. The difference between
    > low and high density chips, was the width of the
    > multiplexed row and column addresses. A high density
    > chip had one more address bit, than there were drivers
    > on the Northbridge (of chipsets like 440BX). As a consequence,
    > only half of a high density chip could be addressed by
    > the Northbridge. A module with 8 chips would be half
    > recognized, while a module with the "lower density" 16
    > chips in two banks, would be fully recognized. That is
    > why you had to be careful when buying 256MB SDRAM for
    > 440BX motherboards.
    >
    > Paul
    job, Aug 2, 2006
    #3
  4. job

    Paul Guest

    In article <xU8Ag.207754$>,
    "job" <> wrote:

    > Cool.Great explanation.But,This 64x64 thing and 128x64.Same as 128x4? The
    > link I proved seerms not to go where I thought.
    > Anyway,the dont recommend these for Intel.I wouldn't buy them for anything
    > anyway.I was just curious. Alot of people just look at price when buying,as
    > do I,but I'd like to know a bit more about these things.Thanks Paul.


    The notation 64x64 is perfectly meaningless to me. I don't know
    why they say stuff like that, since it is an imprecise term.
    They might as well tell you the modules are "blue in color"
    as a technical spec, for all the good those numbers do.

    Paul
    Paul, Aug 9, 2006
    #4
  5. job

    Julie Green Guest

    "Paul" <> wrote in message news:nospam-0908060247030001@192.168.1.178...
    > In article <xU8Ag.207754$>,
    > "job" <> wrote:
    >
    > > Cool.Great explanation.But,This 64x64 thing and 128x64.Same as 128x4? The
    > > link I proved seerms not to go where I thought.


    See P.43 and following pages in this document:
    http://www.kingston.com/taiwan/tools/umg/umg2000.pdf
    Julie Green, Aug 9, 2006
    #5
    1. Advertising

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