Questions about dual channel RAM

Discussion in 'Mac Basics and Help' started by GFLPraxis, Jul 4, 2006.

  1. GFLPraxis macrumors 604


    Mar 17, 2004
    I keep hearing about the benefits of dual channel RAM and wanted to ask a question. I've always been in the habit of never buying RAM from Apple because they overcharge so much. Now, someone told me that for dual channel RAM to work they have to be of the same size (okay, duh), type (figured), *and* brand (why?).

    Is this correct?

    If so, should I buy the RAM from Apple? Otherwise, where should I get the RAM to properly match it up? I'm planning to buy an iMac Core Duo during their back to school deal with the free iPod, but I think I'm going to wait until after WWDC, just in case it gets updated.

    Also, which will perform better- two identical 512 MB sticks, or a single 1 GB stick?
  2. dmw007 macrumors G4


    May 26, 2005
    Working for MI-6
    Having RAM run in dual channel mode does offer added performance. Nothing major, but worthwhile if you can. Performance will vary from task to task, but generally around 5%-15%.

    No, you can get paired RAM from other venders- such as Crucial or datamem for instance.

    The two identical 512MB sticks of RAM.
  3. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    However -- two 512;s is a dead end, it maxes the machine at 1 Gb - you'll amost certainly be pulling them out later to upgrade again. 1 x 1 Gb added to the stock 1 x 256 makes 1.25 Gb (a wee bit more space) and although you lose a bit on Dual channel, you gain in future flexibility.

    The other part of the OP's question is: If I buy a 1 x 1 Gb configuration from Apple, will I be able to add a third party 1 Gb to it later to make a matched pair. The answer is: Possibly, but there is no guarantee. To make a Dual Channel pair, the RAM modules have to match for speed and size, but also for composition - that is the number of chips, the organization into Rows and Columns, and the SPD settings. It is possible for 2 modules from different manufacturers to match perfectly -- but since Apple uses 3 or 4 suppliers for RAM and doesn't publish the composition of their modules, its a crapshoot. None of the manufacturers we deal with are prepared to offer a guarantee of matching Apple - coz its a moving target.

    The only 100 % guaranteed way to get a matched pair is to buy two at the same time from the same vendor.

  4. Timepass macrumors 65816

    Jan 4, 2005
    Well reason they normally add same brand to it is because time timing works better.

    But really the best way to do it is buy the ram in pairs because ram you get in the pairs is made in the same batch.

    But really it not to bad.

    The thing that needs to be match are the ram timings and since apple doesnt tell you that harder to do.

    Personally I am with taking the apple ram and replacing it with a matching pair.
  5. GFLPraxis thread starter macrumors 604


    Mar 17, 2004
    What I meant was, if I have the 512 MB that came with my Mac, can I buy another 512 from Crucial of similar specs and expect it to work? And how can I check if it is?

    Would it be better of me to just forget the matching pair and go for 1.5 GB (the built in 512 from Apple + a 1 GB chip) for the same price?
  6. matticus008 macrumors 68040


    Jan 16, 2005
    Bay Area, CA
    No, adding another 512MB module, even with the same timing specifications, isn't likely going to work. In order for interleaving to work properly, the memory essentially has to be physically identical with each other.

    You are better off with more memory than with matched memory in most cases. 1.5GB will outperform 1GB, dual channel or not.

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