Ram purchase all or nothing?

Discussion in 'Mac Pro' started by ncc1701d, Mar 6, 2009.

  1. ncc1701d macrumors 6502

    Mar 30, 2008
    Just called up OWC because I looked on their web site and wanted to find out if you can add 4GB ram pairs to a new Mac Pro (with the original 6x1GB ram). They said not only do they not know (fair enough since they haven't got a new Pro yet), but it looks as though if you want 4GB ram, you have to buy the whole lot or stick with multiples of 2GB.

    Does anyone know if you can

    1) add 4GB to the existing 6x1GB or will the 6x1 GB's have to be removed completely?

    2) can you even just add 1 4GB pair at a time (save save save buy another pair and add, repeat, continue :))

    OWC link here: http://eshop.macsales.com/MyOWC/Upg...2&type=Memory&TI=0236&shoupgrds=Show+Upgrades
  2. shadowfayre macrumors regular

    Jan 17, 2006
    A trekkie! So I have to respond. :)

    No one knows right now how a 4GB stick will work. Nor does it seem officially known on the way the MP will handle additional memory. The census right now is that there are 4 slots (single) 8 (dual). the first 3 (6) be run in tri-channel mode while the forth will run in single-mode (slower).

    If that holds true, and the 4GB works, then you will have the 6x1GB sticks running at tri-channel and the one 4GB and later the second one for the other processor, will run in single-channel.

    I would have to agree with their theory since every board shown during the past year based on this infrastructure has 4 slots. Why 4? Who knows. I would have prefer to to have 6 per processor, so all were at tri-channel. Maybe it is similar to PCIe lanes. There are just so many available lanes for memory to the processor?!?
  3. Umbongo macrumors 601


    Sep 14, 2006
    No it's just Apple being Apple.

    However as the only DDR3 1066MHz 4GB ECC modules are registered (RDIMM) rather than unbuffered (UDIMM) like the 1GB and 2GB DIMMS Apple are selling they may not work. I doubt you can mix Registered and Unbuffered memory.

    edit: I stand corrected. There are going to be 4GB DDR3 ECC UDIMMs. Hynix list them as not in mass production while Samsung do list them as in mass production, but they do not seem to be in retail channels.
  4. nanofrog macrumors G4

    May 6, 2008
    The 4th DIMM slot should be shared with one of the other three channels. This would allow for 3 channel operation, even if all 4 are used. The switched DIMM's do operate a little slower due to latency, but it won't be that bad.

    If adding the 4th DIMM reduces the machine to single channel operation, that would be incredibly stupid. Intel would have certainly taken this into consideration when designing the architecture. Which is why board with 2 or more DIMM's per channel are in fact operating in a switched (interleaved) mode.

    I'm thinking that the "single channel" description is confusing people, as it's describing that particular DIMM sharing a channel. Not how it handles memory throughput when additional channels are utilized as well.

    Most manufacturers seem to be planning to release their products at the same time Intel formally releases the Xeon 5500 and 3500 series parts. So early April. ;)
  5. ncc1701d thread starter macrumors 6502

    Mar 30, 2008
    Ha! Not many seem to know :) Seen the new trailer?... but I digress :D http://www.youtube.com/watch?v=_Pqc878-jRQ
    OK, so it looks as though I should go for the multiples of 2GB sticks and hope that they can be matched with 4GB sticks when I want to expand... I think.
  6. nanofrog macrumors G4

    May 6, 2008
    Technically possible, but matching might prove difficult. Swapping the stock memory for 4GB matched would eliminate that particular need. Certainly not cost effective though, if you were planning to mix them. (I assume this is the case, given the way you wrote the post).

    For simplicity, and saving cash, you'd likely have to forgo matching mixed sets. :rolleyes:
  7. ncc1701d thread starter macrumors 6502

    Mar 30, 2008
    option a)
    I would rather buy the 6 x 1GB base computer, throw out the 6 x 1GB ram and initially replace with 2 x 4GB. Then, when funds permit, get another 2 x 4GB and so on. But now I don't know if it is possible to do that (one 4GB pair at a time).

    Option b) is to figure out if any mixed pairs is possible and go from there. If mixed pairs are possible, I'd rather get apple 2 x 2GB and add 4GB pairs as funds permit

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