Installing Ram in Early 2008 Mac Pro

Discussion in 'Mac Pro' started by TMR812, Jan 24, 2008.

  1. TMR812 macrumors newbie

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    Aug 13, 2007
    #1
    I have the 2.8 Octo, and I came with the 2x1gb of Ram. This ram was placed with one in riser A, and one in Riser B. I bought 2x2gb of ram from owc, and intend to install it with the 2x1gb for a total of 6gb.

    Yes, I know this isn't an optimal configuration, but I'm doing it anyway :)

    Question: Where do I install it? If what I'm seeing is true, then I should put the 2x2gb in rise A (the upside down one -in slots 1 and 2), and put the 2x1gb in riser B (the bottom one - in slots one and 2)

    Is this correct?

    Thanks,

    TMR
     
  2. 4God macrumors 68020

    4God

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    #2
  3. TMR812 thread starter macrumors newbie

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    #3
    I agree, but I think the manual is assuming that you have 2x1gb, and are adding another 2x1gb. in that case, just move one up, and install the new ones on the bottom.

    However, what if the two new ones are a different size. I've always heard that the larger ones are to go into riser A, and the smaller ones into riser B (Just like the Mac pro memory config sheet has it for the old mac Pro's.

    Have I lost my mind, or does this ring a bell?????

    TMR
     
  4. 4God macrumors 68020

    4God

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    #4
    The manual doesn't clarify wether or not your adding a pair of 1 gig sticks or a pair of 2 gig sticks. I do read though that you must install in matched pairs.
    I have installed the pair the way I think the manual instructs and it is working great for me.

    Also, it seems to differ a little from the old MacPros. I had a 2.66 and I think I know what you're talking about, but it seems to be a little different
    in these newer ones.
     
  5. TMR812 thread starter macrumors newbie

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    Aug 13, 2007
    #5
    Here's the diagram I was referring to. Does anyone know if this still applies to the new 2008 Pro's? Also, is the top riser (the upside down one) riser A?

    Thanks,

    TMR
     

    Attached Files:

  6. TMR812 thread starter macrumors newbie

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    #6
    I agree, the manual isn't real clear on this, and this diagram seems to be more specific. I've installed mine like the diagram, and it's working great. Perhaps it doesn't matter as long as they're paired correctly.

    I used this diagram for the my old pro, but didn't know if the rules have changed with the new machine.

    Perhaps others might have some insight to clear this up for me.
     
  7. 4God macrumors 68020

    4God

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    #7
    Yeah, kinda funny. I went through the entire manual and nowhere does it refer
    to the risers as A or B just top or bottom.
     
  8. TMR812 thread starter macrumors newbie

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    #8
    Oops sorry 4God... I quoted the wrong post in my last reply:confused:
     
  9. TMR812 thread starter macrumors newbie

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    Aug 13, 2007
    #9
    OK, I know that riser A is the top (upside down one), because my 2x2gb is installed there, and my profile confirms it.

    Soooooo, the billion dollar question is... Does the config diagram posted earlier still apply to the new pro's?

    Thanks,

    TMR
     
  10. Peace macrumors Core

    Peace

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    #10
    I would say no. The diagram shown earlier is for the older Mac Pros. My reasoning is my Mac Pro came with 2 1gig sticks. Each stick was in the first slot on each riser.This makes sense in a way. Or whoever built the system put the memory in wrong.

    I added 2 more 1 gig sticks and now there are 2 on riser a ( top ) and 2 on riser b ( bottom ).
     
  11. TMR812 thread starter macrumors newbie

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    #11
    Yep, mine came that way also. So, if you were going to add 2 more 2 gig sticks (instead of the 2 more 1gig sticks), where would you place them?

    TMR
     
  12. awad macrumors member

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    Sep 4, 2006
    #12
    i took out the 1gb stick out of riser A and put it with the second gig stick in riser B, then installed 2 2GB sticks in riser A
     
  13. 4God macrumors 68020

    4God

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    #13
    I did the opposite. It works for me, but then again it probably doesn't matter as long as they're in pairs.
     
  14. hayduke macrumors 65816

    hayduke

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    #14
    The memory testing that I have seen has basically shown that the benefits of placing matched pairs in different slot-pairs on different risers has a very *minor* impact on I/O.

    Any configuration will work and it would take objective testing to determine which configuration is actually faster (ie the speed changes is barely noticeable to the user). That's my current understanding...which, I believe, applies to all MacPros (old and new).
     
  15. pfleischman macrumors member

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    Jan 13, 2008
    #15
    I agree

    I just posted this on another forum, but I think it applies...
    Now after looking up (a lot) I think the information they have provided does not seem acurate about the stock memory. On the diagrams they have listed at http://developer.apple.com/documenta...SW3_1200331177 it clearly shows that each riser has its own connection to the branch of the North Bridge, which if i'm not inept only carries data from each riser at 6.35GBps. I dont get how having all of the slots full on each risers makes it faster with matching memory when the two risers do not talk to each other at all. i'll quote the link "The 5000X features a quad-channel FBD memory controller, with two channels going to each riser card". Just to sum up if i've lost anyone you could have a riser with only two slots on each and it would run just as fast as having a riser with 10 slots on each (sans latency for pushing data across the bus). So I dont understand how they came up with these results, I need to see real world numbers based on their findings, or if someone has the memory could they just post some results???
     
  16. NOV macrumors 6502

    NOV

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    #16
    been reading this on barefeats.com

    can anyone confirm this?
     
  17. ComeOnDieYoung macrumors member

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    Jan 18, 2008
    #17
    bare with me.

    please be patient with me, this is my first desktop mac and first time installing ram.

    I have 6x2gb of OWC ram
    2x1gb of the RAM that came with the mac pro

    What do I do?
    load up A with all 2gb, put the 1gbs at the end of the B card?
     
  18. peejack macrumors 6502a

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    Aug 7, 2007
    #18
    I think im just going to order 2x2GB and take the stock 1gbs out so i just have 4.
     
  19. bigbird macrumors 6502

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    #19
    That is exactly correct. Riser A (top) 2-2-2-2
    Riser B (bottom) 2-2-1-1
     
  20. Umbongo macrumors 601

    Umbongo

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    #20
    This is also my understanding, the problem has arisen I believe because of people over emphasising optimal memory configurations.

    Note that you should position them in the same slots your 1GB DIMMs are currently in.
     
  21. MaddMacs macrumors 6502

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    #21
    I think what matters the most is that the two 1gb sticks should be on the same riser.
     
  22. kittiyut macrumors regular

    kittiyut

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    #22
    And the reason being?
     
  23. pfleischman macrumors member

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    Jan 13, 2008
    #23
    From apple's dev site

    "The 5000X features a quad-channel FBD memory controller, with two channels going to each riser card" this means the risers do not talk to each other, now if the CAS is diffrent that could change the results but diffrent sized dimm's doesn't seem right. Maybe only maybe if you had diffrent sized memory on the same riser it could have an effect but I doubt it.
     
  24. Mr.PS macrumors 6502a

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    Jan 8, 2008
    #24
    How about this? First riser slot 1 and 2 (2 x 2gb sticks), 2nd Riser slot 1 and 2 (2 x 1gb sticks). Does this look correct for 6gb (2 x 2gb and 2 x 1gb)?
     
  25. pfleischman macrumors member

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    Jan 13, 2008
    #25
    I'm setting it up that way

    I going to install it that way. I dont know if that makes you feel better...
     

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