Can anyone confirm performance plus or minues for matched and non-matched RAM?

Discussion in 'Mac Pro' started by tivoboy, Jan 24, 2006.

  1. tivoboy macrumors 68040

    May 15, 2005
    So, my 20" imac should be here tomorrow, but I haven't yet order an additional RAM chip for it yet.

    Some people say, more is better, ala 1GB is going to get the unit to 1.5 GB, which is a heck of a good amount of RAM for a desktop.

    Other people say, "must be matched" and that adding 512 MB, to the existing 512 MB is better than adding 1 GB to the 512 MB, since it would then be "matched"

    Honestly, does anyone have BOTH chips available that can test this out? Or, is there a testing group that can test it in whether or not matching gives a true additional bonus, OR non paired memory gives a TRUE performance HIT?

  2. jsw Moderator emeritus


    Mar 16, 2004
    Andover, MA
    I don't have the specs for you - especially for the Intel systems - but my 17" iMac ("free" as part of the Developer Transition Kit exchange program) is getting a 1GB stick installed Thursday (the iMac arrives tomorrow, the RAM Thursday).


    Matched RAM is faster than unmatched RAM, but the numbers depend on the platform. I've never seen anything indicating that it is a huge improvement in real-world application times except for things which are very RAM-intensive, like Photoshop, and, even there, I don't recall seeing huge gains.

    On the other hand, unmatched RAM is vastly faster than hard disks are, and so, based upon current RAM usage in my development setup, which tends to peak above 1GB often, I feel that I'll be better served by that additional 512MB of RAM than I would be by matched pairs.

    If you consistently use less than 1GB of memory, the 512MB stick will likely be, sometimes, a bit faster.
  3. T-Stex macrumors 6502

    Jan 15, 2006
    I think the "matched pairs" applies more in the case where you'd be using 1 x 1GB OR 2 x 512MB. In that case, the matched pairs would give you a performance advantage.

    In your case, however, I think you'll see a bigger performance gain by adding 1GB, up to 1.5GB, rather than matching the 512MB stick. I'd definitely go for more RAM rather than matching the original stick.
  4. joecool85 macrumors 65816


    Mar 9, 2005
  5. nutmac macrumors 68040

    Mar 30, 2004
    Matching memory pair for dual-channel consists of matching speed and configuration as well as capacity. For instance, adding 512 MB DDR2 PC2-4200 4x32 double-sided SO-DIMM or 512 MB DDR2 PC2-5300 8x64MB single-sided SO-DIMM to an iMac with 512 MB DDR2 PC2-5300 4x32 double-sided SO-DIMM will let it operate at single-channel.

    In a nutshell, dual-channel moves memory from both modules at once. Since channel to each memory module is 64-bit wide, it is sometimes simplified as 128-bit memory access (a bit misleading). Operating DDR2 PC2-5300 (667 MHz) memory in single-channel will peak at 5.3 GB/sec and 10.6 GB/sec in dual-channel. But we are talking about peak bandwidth here and memory isn't the only variable to computing experience. Depending on what you do, your iMac will perform anywhere from 5 to 25% faster in dual-channel (I would say 10% would more typical).

    1.5 GB in single-channel vs. 1 GB in dual-channel is tricky, however. When it comes to Mac OS X, more RAM the better. Obviously, if your applications are using lots of memory, 1.5 GB will be a lot better. And you can always replace 512 MB with a matching 1 GB module later on.
  6. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Has anybody seen Apple documentation yet that says in so many words whether the iMac intel supports Dual Channel memory access?
  7. nutmac macrumors 68040

    Mar 30, 2004

    iMac Technology Overview (see page 14).
    MacBook Pro Technology Overview (see page 14).
  8. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Thanks nutmac.

    You'd think that Apple would hev that indexed in their Search by now...
  9. alienex macrumors regular

    Feb 11, 2005
  10. tommytahoe macrumors newbie

    Apr 13, 2006
    anyone know why my unmatched pairs of SDRAM are not working together in my Intel?

    hey guys,
    I'm a little late to this forum party (8 months), but here goes.
    I've run into a problem the last couple of days. I have a 17" Intel core Duo (early 2006 model), and it came with 1 memory module of 512 MB, with all the specs iMac's Intels need (DDR2 SDRAM, PC2-5300, 667 speed, 200-pin, and so on). My new memory module meets these specss to a tee.
    Yet when run together, the old in the new in the top and bottom slots (or vice versa), the iMac doesn't boot and i get the blank screen and dreaded blinking white light at bottom-right (incompatibility).
    I've spoken with apple help, and apparently this memory should be fine, even though it forces the mac to run on single-channel mode since the modules are of different size. I've already decided this is fine by me. I'm not an animator or anything, so until I bump up to 2GB total, 1.5 in single-channel suits me fine.
    That is, if the damned things would operate together. Like oil and water. Individually they are fine. But together...

    Any ideas, folks? is there a way for me to get "under the hood" to set the imac to single-channel. Could this be something to do with different manufacturers of the modules, even though all the specs match?
    Also, the apple cust. service guy was telling me the PC2-5300S. I had never, ever heard of the "S" at the end. Maybe hye's new. i thought there were PC-5300, PC2-5300, etc, but not one that had to end in an "S". Even the apple website doesn't require this kind of memory.

    Thanks for the help,

  11. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Simple, Tom
    Your new chip is either defective or not compatible, even though the top level specs are nominally corrrect. There are a bunch more things to compatibility than you will see published in the specs. The SPD settings are incorrect, or it is not voltage-stable, or the timings are off or something.

    Send the module back to the vendor for replacement or refund. Ask for a module that is tested on Macs and guaranteed compatible with your machine, If the vendor is not prepared to guarantee Mac compatibility, then take the refund and switch to a vendor who does.

    It is NOT a single/dual channel issue. It's a bad chip.

  12. tommytahoe macrumors newbie

    Apr 13, 2006
    Thanks CanadaRAM,
    sounds like I should do this. I was just trying to get the absolutely correct diagnosis to make sure there wasn't some fix I could do on my end (short of manufacturing my own memory stick)

    But you still think it is a bad chip, even though I am typing right now, with the new 1 GB stick in the top slot of my iMac? It works fine on its own, but the compatible for macs thing you were referring to was compatible to work with what's in there right?


    Snowing on BC mountains yet?
  13. tommytahoe macrumors newbie

    Apr 13, 2006
    just wanted to say that it is all fixed. Turns out that I did not have the memory module fully "seated" in the memory slot after all. I guess since it was new it was a bit rougher going in, even though I thought I had it in deep.

    ** Take note, everyone: you may have myriad issues with your RAM and motherboard/mac, and no doubt all these guys probably can help.
    But make sure before you go through my whole thing, that the RAM's actually in there tight. (Don't hurt yourself, or the memory stick, of course).
    I was looking for an answer, and the reason THAT was so frustrating is that I wasn't gonna find it cos it wasn't there. It was right in front of me. All about gettin' those buggers in solid.

    Thanks for the help, CanadaRAM.

Share This Page