Mac Pro DDR3 memory in threes?

Discussion in 'Mac Pro' started by ajbrehm, Mar 5, 2009.

  1. ajbrehm macrumors 6502

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    #1
    I heard that it is better to equip a current Mac Pro with memory in threes, i.e. 6 GB made up of 3x2 GB rather than pairs or fours (i.e. 8 GB made up of 4x2 GB).

    Not knowing the specific advantages I am wondering if anyone can advise?

    I am planning to buy a Mac Pro, one CPU, slowest possible, 6 or 8 GB of memory, 1 TB disk, and the 512 MB ATI video card. Is that a good idea or should I seriously consider a second CPU, more memory, two smaller hard disks instead of one?
     
  2. Charlie.naylor macrumors newbie

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    Oct 29, 2007
    #2
    I talked to an apple person specifically about this.

    He said, despite that the ram is triple buffered, adding another stick of ram into the fourth slot wont hamper performance.

    i wasnt sure at first but i guess having more ram offsets any possible performance hits.
     
  3. Tallest Skil macrumors P6

    Tallest Skil

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    #3
    RAM can be installed both in triads and in pairs.
     
  4. Umbongo macrumors 601

    Umbongo

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    #4
    No it's that the first three still get tri-channel performance and the fourth just gets single.

    Single channel memory bandwidth is 8.53GB/s, dual 17.06GB/s, triple 25.6GB/s.
     
  5. ajbrehm thread starter macrumors 6502

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    #5
    So in this case 8 GB is better than 6 GB because the 6 GB will use the faster speed and 2 GB will be slower?

    I think I like that.

    I wonder what discount my ADC Select membership will give me. :)
     
  6. Umbongo macrumors 601

    Umbongo

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    #6
    I don't know how memory management works though, as in if that single channel 2GB dimm is used when the faser 6GB is tapped out or not. I'd buy 6GB and see how you get on, you can always add another cheap 2GB stick later.
     
  7. ajbrehm thread starter macrumors 6502

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    #7
    Yes. Even 2 GB sticks cost less outside Apple.

    Now I am worrying about the second CPU. :)

    It's too easy to spend more on these things, isn't it?
     
  8. Charlie.naylor macrumors newbie

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    #8
    ah okay, thats more clear, thanks very much! :)
     
  9. Umbongo macrumors 601

    Umbongo

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    #9
    Yep even with 3rd party upgrades once you start adding drives and memory the costs pile up :)
     
  10. ajbrehm thread starter macrumors 6502

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    #10
    I think I'll uncase my external Firewire disks and add them to the computer.

    Do you think it makes sense to Timemachine to an internal disk and then copy the contents of that disk to an external disk every week or so?

    I am thinking:

    Drive 1: Mac OS X, home directories, applications, Timemchines to drive 2

    Drive 2: Timemachine backups, virtual machines

    I don't want virtual machines to be backed up, obviously (big files that change all the time) and currently keep them in /Users/Shared which I excluded from Timemachine. I assume the above model represents a good balance for disk usage. But drive 2 should then be bigger than drive 1. Oh my!

    Maybe I should add a third disk.

    I am so looking forward to this, I almost don't care about the cost any more.
     
  11. nanofrog macrumors G4

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    May 6, 2008
    #11
    I would think the 4th stick is a switched bank. That is, Channel A has 2 DIMM slots, and the ICH10 switches between the DIMM's when needed. It would still allow all 4 DIMM's to be filled, and operate in 3 channel mode. Albeit a little added latency from switching to DIMM0 or DIMM1 on Channel A.

    That's what I gathered from the specs anyway.
     
  12. Umbongo macrumors 601

    Umbongo

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    #12
    Ok good to know. I hope someone like Rob (barefeats) can test this.
     
  13. imikejackson macrumors newbie

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    Mar 5, 2009
    #13
    I am trying to find out the complete specs for the DDR3 Ram used in the new Mac Pros. OWC has 32 GB for $5,000 USD which seems a bit, uh, much. I then found 4GB sticks on Crucial's website that would take that total down to about $1,500 USD which is better.

    The specs from Crucial's site are the following:
    4GB, 240-pin DIMM, DDR3 PC3-8500 memory module
    CT51272BB1067
    Module Size: 4GB
    Package: 240-pin DIMM
    Feature: DDR3 PC3-8500
    Specs: DDR3 PC3-8500 • CL=7 • Registered • ECC • DDR3-1066 • 1.5V • 512Meg x 72

    All from <http://www.crucial.com/store/partspecs.aspx?IMODULE=CT51272BB1067>

    Now, if you go to www.macsales.com and go through the links all they say is Mac Pro certified, 32GB for $5,000. What if I only want 4x4GB of ram so I can expand later?

    That is a huge price difference and I am sure there are some sort of technical difference between the two Ram vendors products.

    Is Triple Channel implemented on the ram dimm or in the memory controller? Dunno

    Any help or clarifications would be great.

    Thanks
    Mike
     
  14. chewietobbacca macrumors 6502

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    #14
    Triple Channel is based on the memroy controller, not the RAM DIMMs themselves. Go with Crucial, they're a great company. Basically, as long as the RAM is compatible, it'll work
     
  15. nanofrog macrumors G4

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    #15
    I'd go with Crucial. OWC's price is way too high. Both are CL = 7, and I'd expect OWC's offering to be Registered as well. No difference this time, as it's not like the FB-DIMM in the '08 model, that used a different heatsink.

    BTW, which version of '09 are you looking at?
    I ask, some models can actually support 1333MHz memory, as it was built in by Intel. ;) ('09 Octo X5550 (2.66GHz) and X5560 (2.93GHz) can).

    The channel management is handled by the memory controller, IMC, but the DIMMS play a part as well (location only), as each channel has it's own dedicated lanes. All DIMM's do not share a single bus. In the case of the '09, one of the DIMM's does share a channel, and the IMC switches between them. (It still operates in 3 channel mode if all slots are filled).
     
  16. Sun Baked macrumors G5

    Sun Baked

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    #16
    ICH10?

    I thought the memory controller moved from the ICH controller to the CPU.
     
  17. chewietobbacca macrumors 6502

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  18. imikejackson macrumors newbie

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    Mar 5, 2009
    #18
    I am looking at the 2.66 model with the ATI card in addition. I am going to be doing some long term (weeks at time) scientific calculations so I need as much memory as I can get. CPU speed is secondary but I'll take what I can get.

    Mike
     
  19. nanofrog macrumors G4

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    #19
    Oops. I meant IMC. :eek:
     
  20. imikejackson macrumors newbie

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    #20
    Does OWC actually list the specs for their memory somewhere so I can compare the two dimms? The other question is can a system run unregistered or registered memory? As long as it is ECC and the rest of the specs match?

    I guess I would like to see that Crucial's memory DIMM is the _exact_ same (spec wise) as OWC's memory dimm. Just for some assurances.

    Mike
     
  21. nanofrog macrumors G4

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    #21
    OWC has it listed here. No mention of Registered or Unbuffered though. :confused: I would have thought they'd include that information.

    You might want to get in touch with them and find out for certain.
     
  22. Umbongo macrumors 601

    Umbongo

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    #22
    Do the new Mac Pros support Registered memory? I assume they do but is there any official confirmation?
     
  23. nanofrog macrumors G4

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    #23
    I know Intel included support for it, but I haven't seen anything official from Apple. Nor on the ability to use 1333MHz memory with the X5550 & X5560.

    However, my instincts tell me the 32GB option would be Registered, and 1066 was selected for cost & a unified parts sustem.
     
  24. Tallest Skil macrumors P6

    Tallest Skil

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    #24
    I assume that once OWC gets their machines, they will not only start selling configurations other than those that Apple sells (because they will have tested others), but that they will also sell 1333MHz RAM if they test it and find that it works.
     
  25. imikejackson macrumors newbie

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    Mar 5, 2009
    #25
    Well let's hope something cheaper than OWC and Apple comes along. The Crucial RAM looks promising but I would feel a whole lot better if I could compare the specs between the 2 DIMMS.

    Mike
     

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