Amount of additional RAM and Distribution of it

Discussion in 'Mac Pro' started by Ivo10, May 31, 2009.

  1. Ivo10 macrumors newbie

    Joined:
    Aug 23, 2008
    #1
    Hi,

    I wanted to dedicate a separate thread to this question, since I think it's a big enough topic of its own.

    1. How much RAM is enough? Obviously the more the merrier, but after a point it gets too costly, and I'm sure there are diminishing returns.

    What do you think about 12 (6x2GB)?

    I will be doing HD video editing, Audio recording in Pro Tools and Logic, and Photoshop processing.


    2. Distribution - does distribution of RAM affect performance in any way? For example, is having 6 slots filled in with 1 GB ram sticks, and the other 2 filled with 3 GB sticks a good idea? Or is it better to distribute them evenly? Do certain slots get preference?

    Thanks!!
     
  2. GoCubsGo macrumors Nehalem

    GoCubsGo

    Joined:
    Feb 19, 2005
    #2
    Well first 12gh sounds good. But you have to have matched pairs. You cannot gave 6 1gb sticks on the first riser and 6 gb (2gb sticks each) on the next riser.
     
  3. Tallest Skil macrumors P6

    Tallest Skil

    Joined:
    Aug 13, 2006
    Location:
    1 Geostationary Tower Plaza
    #3
    640k ought to be enough for anyone. ;)

    You have to have matched pairs in the 2006 and 2008 Mac Pro, but not the 2009.

    The Nehalem Mac Pro can have singles, pairs, and triads, I believe. I could be wrong about the singles.
     
  4. gugucom macrumors 68020

    gugucom

    Joined:
    May 21, 2009
    Location:
    Munich, Germany
    #4
    To achieve best speed the RAM has also to be fitted in a particular way. If you fill only the first two RAM banks of both risers for instance it will be faster. So if you fit 4 times 4 GB it will be faster than 8 times 2 GB.
     
  5. Loa macrumors 65816

    Loa

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    May 5, 2003
    Location:
    Québec
    #5
    Haha, good idea Bill...
     
  6. Flash SWT macrumors 6502

    Flash SWT

    Joined:
    Mar 14, 2009
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    Houston, TX
    #6
    We need to be careful since RAM is vastly different in the 2009 Mac Pros from the older models. All evidence with the new Early 2009 models points to having RAM installed in 3s produces the fastest (on paper) results.
    http://barefeats.com/nehal02.html
     
  7. Loa macrumors 65816

    Loa

    Joined:
    May 5, 2003
    Location:
    Québec
    #7
    Hello,

    We also have the info that it has to be installed in pairs... so nothing else but groups of 6 should be considered, which means that quads are doomed...

    On the other hand, if you read Barefeats texts, you see that in actuality, having 8GB (4X2GB) is better than 6GB (3X2GB) because very few (none?) apps saturate the memory bandwidth completely...

    Loa
     
  8. Roy macrumors 6502

    Joined:
    Jul 6, 2006
    #8
    You lost me on your logic. 2 X 4GB is a pair and 2 X 4GB is a pair. So then how is a quad doomed if the ram has to be installed in pairs (you said the "pairs" part. I didn't)?
     
  9. Flash SWT macrumors 6502

    Flash SWT

    Joined:
    Mar 14, 2009
    Location:
    Houston, TX
    #9
    You need at least one pair with the 2009 models on the 8-cores (split between processors) but you can install single sticks on the 4-cores. However the manual specifically mentions using three sticks of RAM in an 8-core so ...

    Right, which is why I specified "on paper." But since the OP asked about 6x2GB we are talking about an 8 core model. My post was to clarify that gugucom's information is not accurate for the 2009 models as it is for the 2006/2008s. This is important now that the newest Mac Pros have different RAM specifications and instructions from the earlier models. We need to make sure we don't misinform members who are new to the Mac Pro and as such will more times than not be asking about current 2009 models.

    Back to the OP:

    I think 2GB sticks are currently the sweet spot between quantity and price. You can hit 16GB relatively cheaply and will save yourself money over buying the 4GB sticks unless you really need more than 16GB of total RAM right now.

    That is what I did, BTO'ed the machine to come with 4x2GB and will be adding additional 2GB sticks later. This keeps you from having 1GB sticks you can't use.

    First there are only 1GB, 2GB and 4GB sticks available. It seems you cannot mix third-party 4GB sticks with other sizes but I don't think anyone has reported problems mixing 1GB and 2GB sticks. If you did, I'm pretty sure the two 2GB sticks should be in slots 1 and 5 with the 1GB sticks in 234 and 678.

    However note that the memory section of the manual, available here as an 11MB PDF, page 55:
    http://manuals.info.apple.com/en_US/Mac_Pro_Early2009_4707_UG.pdf
    contradicts the advice of the built-in Memory Slot Utility as reported here:
    http://blog.macsales.com/517-rtfm-may-not-always-be-right

    I personally think 4x2GB from Apple plus additional third-party 2GB sticks is the way to go at this point ... unless you really need more than 16GB.
     
  10. Roy macrumors 6502

    Joined:
    Jul 6, 2006
    #10

    And what will be the effect(s) if I put a 2GB stick in slot 4, while have slots 1, 2, and 3 filled with 1GB sticks on a 2009 Quad?

    I'm waiting on 4GB modules to come down in price, and they are coming down, so that I can use 3 X 4GB only.
     
  11. Flash SWT macrumors 6502

    Flash SWT

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    Houston, TX
    #11
    I have no clue personally but I assume Memory Slot Utility will pop up and suggest you switch it as noted here:
    http://blog.macsales.com/491-ramp-up-your-new-mac-pro
     
  12. VirtualRain macrumors 603

    VirtualRain

    Joined:
    Aug 1, 2008
    Location:
    Vancouver, BC
    #12
    No one is really sure what happens in terms of memory bandwidth... If you fill all four slots there's two possible outcomes (unfortunately the Intel documentation is not clear):

    1. The first three slots run interleaved (tri-channel) and the last slot runs non-interleaved (single-channel).

    2. Slots 1 and 3 are interleaved and 2 and 4 are interleaved giving you dual-channel performance for all RAM.

    In your case, I'm not sure what would happen because a non-symmetric amount of RAM would impact scheme #2 above if that's what happens when all slots are used.

    At any rate, as others have pointed out, memory bandwidth should probably take a back seat to the amount of RAM if you have to make a choice between the two... pick more RAM vs. maximizing performance of a smaller amount. However, 3x4GB sticks would be ideal as it would provide the best of both. Like you, I plan to upgrade to this when the price is right! :D
     
  13. nuvolino macrumors newbie

    Joined:
    Oct 2, 2006
    #13
    ok just to let you know you are actualy wrong with this in tests having all 8 slots filled is better then the same capacity set in just 4 it is also more crutial when i comes to the 8 core macpros see below

    http://eshop.macsales.com/Reviews/Framework.cfm?page=/Benchmarks/macproearly08ram/article.html
     
  14. gugucom macrumors 68020

    gugucom

    Joined:
    May 21, 2009
    Location:
    Munich, Germany
    #14
    I take away from this tread that memory optimization varies for 4 vs. 8 cores and Nehalem vs. other processors. So one must specify which model one wants to optimize memory config for.
     
  15. Ivo10 thread starter macrumors newbie

    Joined:
    Aug 23, 2008
    #15
    Thanks for the input guys. I've ended up going 6x2GB, leaving me with two slots for upgrade options should I need them. However, from what I've gathered from this thread and other advice is that with 12GB on board I should be more than set, so we'll see!
     
  16. GoCubsGo macrumors Nehalem

    GoCubsGo

    Joined:
    Feb 19, 2005
    #16
    I had no idea about that! That's good in many ways but now I'm curious how efficient the memory is because on paper it reads as terribly inefficient. What changes so much that it would allow for unmatched pairs to be used and are matched pairs still better?

    What MP do you own?
     
  17. Roy macrumors 6502

    Joined:
    Jul 6, 2006
    #17
    I wonder where the definitive answer could be found as to whether or not this is correct? Any ideas? If true, then that's something that definitely would be good and good to know.
     
  18. Loa macrumors 65816

    Loa

    Joined:
    May 5, 2003
    Location:
    Québec
    #18
    Maybe I should have added a :) to make things clearer... Groups of three + groups of two = groups of six.

    Was a joke! ;-)

    My comment on RAM saturation, on the other hand, is more serious.

    Loa
     
  19. Ivo10 thread starter macrumors newbie

    Joined:
    Aug 23, 2008
    #19
    2009 :D
     
  20. nittany4 macrumors newbie

    Joined:
    Jun 22, 2006
    #20
    adding a 2g stick?

    Does anyone have an answer to this? I was planning on popping a 2gb module into the empty slot on my new mac pro, but the info floating around is quite confusing...

    any practical experience of 5gb (3 x 1gb; 1 x 2gb) on a 2009 Quad would be great

    THANKS!
     
  21. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #21
    It drops down to dual channel operation. You may not notice any change in performance though, depending on what you do specifically (usage pattern).
     
  22. nittany4 macrumors newbie

    Joined:
    Jun 22, 2006
    #22
    Thanks, I guess the simple question is... will i see any benefit at all to adding the 2gb? or am I better off returning the ram? I guess I'm really old school and think if there's an empty slot and I can stick 2gb in there for $40, why not???

    And if these machines run so much better with ram in 3s, why 4 slots??

    Here's what I do out of the usual surfing, email, music, etc.

    Amateur Photoshop and iMovie; DVD rips; serving 2 Apple Tvs; Illustrator

    thanks again!
     
  23. Boneoh macrumors 6502

    Boneoh

    Joined:
    Feb 27, 2009
    Location:
    So. Cal.
    #23
    When I upgraded my 09 MP, I ran the memory benchmarks at both 12 and 16 gb. The test were run using diglloydTools Stress Test v 1.1.0 64 bit.

    With 12 gb, 6 x 2 gb the max memory speed was 10,421 MB/sec.
    With 16 gb, 8 x 2 gb the max memory speed was 9,024 MB/sec.

    IMO the extra memory is the best way to go. Memory access is several hundred times faster than disk, so if you run out of memory, your disk access is going to quickly eat up the extra memory bandwidth. Also, OS X does a good job of using memory to cache applications.

    You mileage may vary :)
     
  24. TK2K macrumors 6502

    TK2K

    Joined:
    Jun 4, 2006
    #24
    Mac pro has tripple channel ram, meaning each cpu can give a full channel of ram to a stick... long story short occupy 1-6 for best performance

    see here
    http://www.grabup.com/uploads/433591c8f9d8704a000dd5c504b8c40b.png

    or http://manuals.info.apple.com/en_US/Mac_Pro_Early2009_Memory_DIMM_DIY.pdf
     
  25. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #25
    I think you'd be better off going ahead and adding in the extra memory. :) You're described usage would benefit more with the increased capacity rather than going for max bandwidth.
     

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