Re: RAM voltage

Discussion in 'Computer Information' started by Paul, Apr 2, 2010.

  1. Paul

    Paul Guest

    James D. Andrews wrote:
    > "James D. Andrews" <> wrote in message
    > news:hp51g1$2516$...
    >> Trying to choose RAM for a new mobo - a BIOSTAR MCP6P M2+ running an AMD
    >> Sempron.
    >> (This combo was picked primarily for PRICE, but also considering known
    >> compatibility, other factors, and hundreds of positive reviews)
    >> So, the problem I'm having in selection is picking RAM with consideration
    >> to voltage.
    >> I couldn't find RAM voltage specs on the Biostar site.
    >> A couple people stated that the voltage defaults to 1.95V
    >> Do I need 1.95 and above or 1.95 and below?
    >> The long list of chips that meet my other needs and qualifications ranges
    >> from 1.8V - 2.2V

    > Whoops! I forgot to mention, I'm looking at DDR2, either 800 or 1066
    > 4GB (2x2GB)

    All memories "operate" at 1.8V (for DDR2), because that is the JEDEC
    agreed standard. Enthusiast memory may fail to meet timing at 1.8V,
    so the manufacturer may say "meets timing at 2.1V". But all DDR2 should
    do something, when 1.8V is applied.

    You would hope, that if a memory product is in that situation, that the
    SPD would not call up the specified timings. For example, say a memory was
    DDR2-1066 6-6-6-18 at 2.1V. For that memory to start without crashing,
    the "top speed" shown in the SPD might be DDR2-800 6-6-6-18, which would
    represent a slightly relaxed set of values (easier for the memory to meet).
    That allows the user to get into the BIOS, the first time the product is
    used. If the user never entered the BIOS, then the product would stay
    running at DDR2-800 forever.

    Once the user is in the BIOS, they look at the piece of paper that
    accompanied the product, that claimed it was DDR2-1066 6-6-6-18 at 2.1V.
    The user would then dial those values in manually, and test. In other
    words, the SPD is designed to *not* represent the spec for the RAM,
    in order that the motherboard will start up the first time. That is
    to get around the "startup problem".

    Your board supports: 1.950V (default), 2.000V, 2.050V, 2.100V.

    It is going to start at the default value the first time, and then you can
    crank it up.

    I would not buy a memory product with a stated voltage need of
    more than 2.1V to meet timing, as your board doesn't go any higher.

    And if you bought a 1.95V memory, that would guarantee the stick
    would meet timing, no matter what is stored in the SPD.

    This kit is in the right ballpark. The difference between 1.95 and 2.00
    is small enough, that this is likely to work no matter what is in the
    SPD chip on the DIMM.

    Cas Latency: 6 Voltage: 2.0V Dual Channel 6-6-6-18 F2-8500CL6D-4GBNQ

    and this one needs too much voltage to meet its specified timing,
    so you'd need to relax the timing or frequency to make it work
    on your 2.1V max board.

    Cas Latency: 5 Voltage: 2.2V - 2.4V Dual Channel 5-5-5-15 GX24GB8500C5UDC

    Now, I found this comment on another site for the GX24GB8500C5UDC product.

    "The SPD's default this RAM to safe DDR800, but with a few tweaks in the BIOS,
    we are smokin"

    That means the 2.2V DDR2-1066 RAM, starts at DDR2-800, and by doing so,
    it would need less voltage to start. It would likely work well enough that
    it would start right away at your default 1.95V. But the problem is,
    your board only goes to 2.1V, so you couldn't dial in the exact
    numbers on the box. If you wanted to use that 2.2V RAM, perhaps
    you'd set the timing to 5-6-6-18 or something and retest. Then
    try 6-6-6-18 and test again with memtest86+ and so on.

    The reason there is a range of voltages on that second product, is
    the first voltage is the one to meet timing. The second voltage
    is the maximum recommended voltage. And since you can download
    memory datasheets from the memory chip manufacturers, you can
    see that their "absolute maximum" voltage roughly agrees with
    what the DIMM maker is listing.

    When a single voltage is listed, like the 2.0V RAM, they aren't
    listing the absolute max. If you can see what brand of chips is
    being used, you can look up the absolute max for them yourself.

    Some enthusiast memory, contains additional information in the SPD.
    The JEDEC spec, doesn't allow for "enthusiast voltage" as a parameter.
    The specification extensions (there are a couple pseudo-standards), allow
    both timing and voltage to be specified. But the motherboard BIOS
    must support such a scheme, for it to work. If you mixed such
    a stick, with a BIOS that doesn't read that info, you'd be no
    better off than before. Or perhaps even worse off, depending on
    how cleverly the SPD is coded.

    With the conventional SPD scheme, as long as they relax the timing,
    and don't write the rated values in the SPD, then the user can dial
    in the values manually. That defeats the purpose of the SPD (which
    is to automate the process), but solves the problem of enthusiast
    products needing way too much voltage.

    On "non-enthusiast" RAM, say a product that claims to run at 1.8V,
    the operation at 1.95V is not going to hurt it. That is far enough
    below "absolute max" to not affect service life. And the little bit
    of extra voltage helps ensure the motherboard doesn't crash when it
    starts up the first time.

    This one, for example, is specified at 1.8V, which means it is going
    to start in whatever motherboard it is plugged into. One user got this
    to work on an Intel board, but not an AMD. Go figure... Always
    read the reviews, for any quirks. It is how I shopped for RAM
    the last time, and ended up selecting a different brand as a
    result. If the reviews show a lot of DOAs or the like, then
    why bother ? The only way a manufacturer can cut costs, is to
    reduce test time. So the review comments are important. Don't
    just read the summary numbers at the top, read the individual
    comments. For example, if a memory product "burned my DIMM slot",
    I wouldn't touch the product with a barge pole, no matter how many
    other glowing reports there were.

    Paul, Apr 2, 2010
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  2. Paul

    Paul Guest

    James D. Andrews wrote:

    > Paul,
    > Thank you very much.
    > And yeah, I always use the reviews to make my decisions. I don't want to
    > pick a product of any kind that 4/5 people hate, and so on.
    > I also pay attention to what the odd complaints are, such as when someone
    > complains about a product not working the way they want it to when they knew
    > ahead of time it doesn't work that way (e.g., complaining the single core
    > processor they bought on sale isn't quad).
    > Thanks

    With regard to your other comments about the AMD site, and figuring out
    what a processor supports - I agree, their documentation is a shambles.


    AMD processors have the memory controller on the processor itself.
    The speed handled is a family characteristic. A general trend, is
    if the motherboard has four memory slots, the two slot configuration
    usually runs one frequency step above what the four stick configuration can
    do. Your board only has two slots, so that is the only configuration
    choice you've got.

    You also have the limitation, of up to a 95W processor. The Vcore on the Biostar
    motherboard, only has three phases. Now, if they didn't support split plane
    power (separate power for IMC and Vcore), I suppose then the board would
    effectively be AM2, and then the memory would be stuck at DDR2-800. If one
    phase powers the IMC, and two phases power Vcore, then the next speed up
    should be possible.

    This AM3/AM2+/AM2 has DDR2 DIMM slots, and the description says

    "*Due to AMD CPU limitation, DDR2 1066 is supported by AM2+/AM3 CPU only."

    And that motherboard has only two DIMM slots, which is why they don't have
    to distinguish between two slots versus four slots.

    This AM3 board with DDR3 memory...

    "Memory 2 x DIMM, Max. 8 GB, DDR3 1800(O.C.)/1600(O.C.)/1333/1066"

    So in that case, DDR3-1333 is max speed with two sticks, and higher
    speeds are by overclocking.

    If you have an AM2 processor, that kind of processor has one power
    plane for both Vcore and the memory. AM2+ and AM3 are split plane.
    AM2 supports DDR2-800. AM2+ goes to DDR2-1066, AM3 goes to DDR3-1333.

    Your Sargas Sempron 140, is AM3. On a DDR2 motherboard, it should
    be able to do DDR2-1066 (while on an AM3 motherboard with DDR3 slots,
    it would be DDR3-1333 without overclocking. If the processor was plugged
    into an older AM2 motherboard, the motherboard would need a BIOS update,
    and the RAM interface would likely run DDR2-800.

    The thing is, you don't have to worry. You can buy DDR2-1066 RAM,
    and it will happily run at DDR2-800. So it isn't like you have
    to throw the RAM away, if my previous paragraphs are wrong.


    In the reviews here, for the Sempron 140, I can see at least a couple
    people using DDR2-1066 with that processor. And I don't see any
    comments about being stuck at DDR2-800. Mind you, the difference could
    be the motherboard they're using.


    Now, if we look at reviews for your motherboard.

    "Pros: Supports DDR2-1066 RAM ********************
    this wasn't stated in the item description"

    That implies it does have split plane powering (or it is cheating
    and taking chances :) ). So, go for it!

    While some people have succeeded at unlocking the second core in the Sempron 140,
    I would not count on that. In terms of applications, if a family member
    wanted a computer only for Microsoft Office, I wouldn't feel too badly
    about giving them a single core solution. But if you have video playback
    as a part of the plan, I'd want a bit more headroom, and a dual core
    might be a bit smoother.

    This one is $59 and includes a heatsink/fan.

    Paul, Apr 3, 2010
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