Matched pair DIMMs?

Discussion in 'Apple' started by fishfry, Aug 14, 2004.

  1. fishfry

    fishfry Guest

    I was looking at G5 memory on and found this
    T ... a "matched pair" of DIMMs costs more than two single DIMMS
    separately. Is this

    a) A good thing, because the DIMMs have been specially selected to
    perform better together than an average pair of identical DIMMs? And how
    does that work??

    b) Sounds hi-tech, but is actually the greatest scientific hokum since
    the New Agers started wearing magnets around their wrists?
    fishfry, Aug 14, 2004
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  2. fishfry

    David C. Guest

    This is what Apple says too:

    DDR SDRAM DIMMs must be installed in matched pairs. "Matched"
    in this context means that the two DIMMs have the same
    capacity and speed. A valid pair would be two 512 MB PC2700
    DIMMs, for example.
    Matched pairs, in the sense of same manufacturing batch (what memory
    vendors means when they advertise "matched pairs"), has been known to
    help eliminate flakiness in some overclocked systems, but I don't
    think the OP is planning on overclocking his G5.

    -- David
    David C., Aug 14, 2004
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  3. It's technically possible that they could test all of their DIMMs and
    come up with pairs that are as identical as possible. It's extremely
    unlikely that they'd do so, because this wouldn't actually give you any
    sort of advantage. So time and expense would almost certainly outweigh
    any premium in price they could hope to get.
    Tom Harrington, Aug 14, 2004
  4. fishfry

    Acid Pooh Guest

    Not really. Most ram manufacturers already test their ram--this is
    how they determine which spec it meets. Kingston's valueram, for
    instance, comes from exactly the same batches as their more expensive
    lines, but don't meet some of their classifying specifications.
    Instead of throwing it out, they sell it, as it is still usable,
    though not as fast. Implementing a "matching pair" system would be as
    easy as setting up a database of specifications (which they already
    have) and some relations between entries.

    'cid 'ooh
    Acid Pooh, Aug 15, 2004
  5. I guess it depends on how closely you want the DIMMs to be matched. The
    scheme you describe is common enough, and is what you get already if you
    buy a couple of DIMMs rated to the same speed. Doing this and selling
    them in pairs wouldn't imply any closer matching than what someone would
    get by buying two DIMMs with the same rating separately, so it wouldn't
    warrant a premium price.

    Premium pricing for matched pairs would imply a closer match, say by
    narrowing down the gap between the two to something closer than the
    usual ratings. Say, both modules are 80ns modules, but the matched pair
    was guaranteed to have each within 3ns of the other, instead of just
    somewhere in the 80-90ns range. Normal manufacturer testing wouldn't
    have this information, because there's really no point in testing them
    that precisely. It matters to them that it passes at 80ns, but the
    exact timing where it fails to work is not important.

    However this would of course be of no real benefit...
    Tom Harrington, Aug 16, 2004
  6. fishfry

    Acid Pooh Guest

    I don't know about this. It wouldn't take any extra effort to test
    ram to 80-83 ns as opposed to 80-90 ns. All it would require is a ram
    tester with a more accurate clock. In fact, from what I've seen of
    hardware ram testers, they already report speed to the nearest ns.

    Like I said--they already have the information. All it would take
    would be a database of ram chips and their specs (which they obviously
    already have) and some relations between the specs. With this scheme,
    you don't pick a dimm and wait for a match to be manufactured, but
    pick a match out of the database. Such an operation would a costlier
    to operate, since the manufacturer must keep more ram in store--but
    Crucial, for instance, already does that.

    'cid 'ooh
    Acid Pooh, Aug 17, 2004
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