iMac (Retina 5K, 27-inch, Late 2015) optimal RAM layout

Discussion in 'iMac' started by Zmaran, Dec 16, 2015.

  1. Zmaran macrumors newbie

    Joined:
    Jul 19, 2011
    #1
    So, just received my Crucial 16GB Kit (8GBx2) DDR3 1866 MT/s (PC3-14900) SODIMM 204-Pin Memory and upon doing the upgrade, I replaced the included 4GB ram DIMMs with the new 8GB ones and placed the 4GB ones in the empty slots. Now, this is what it looks like :

    Screen-Shot-2015-12-17-at-1.04.06-AM.jpg

    I tried searching around but couldn't find a definitive answer. I just wanted to inquire from the more informed if this placement is optimal or not? Would it make any discernible difference to plug the 8GB DIMMs to Bank 0s and 4GB DIMMs to Bank 1s? Most of what I could gather from the internet is that it doesn't make a difference. :/
     
  2. April Knight Suspended

    Joined:
    Jul 24, 2011
    Location:
    Olympia, WA
    #2
    I am also interested in this question. I have the exact same scenario as you (ordered iMac with stock 8GB RAM, picked up the Crucial 16GB Kit). I also put them in the same layout as you and have not noticed any poor results, but I want to confirm that that's the best configuration.
     
  3. AlexisV macrumors 68000

    AlexisV

    Joined:
    Mar 12, 2007
    Location:
    Manchester, UK
    #3
    Yep, that's the best config.

    Stock: 4 - 0 - 4 - 0
    Yours: 8 - 4 - 8 - 4
     
  4. ivoruest macrumors 6502

    ivoruest

    Joined:
    Jul 12, 2010
    Location:
    Guatemala
    #4
    Mine's a 2014 with 4x4GB setup. Is this in anyway better or worse than the one you proposed before?

    I mean, I have had some issues with my iMac shutting down due to unexpected problems plus some graphical issues. Is this because of the config or has to due directly with bad memory? (if memory was the case) The Apple Technician claims the computer is fine and passed all of the tests correctly. And couldn't reproduce the graphics issues on the days he had the machine. He explained to me that the issues I was getting seemed more like software related and/or memory.
     

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  5. sabester24 macrumors member

    Joined:
    Jan 30, 2013
    #5
    I'm confused...why does this make a difference? I put my 3rd party 16 GB Crucial RAM kit in the open slots and thought that would be fine.
     
  6. AlexisV macrumors 68000

    AlexisV

    Joined:
    Mar 12, 2007
    Location:
    Manchester, UK
    #6
    The same DIMMS should be in opposite slots so they run in dual channel mode. Not that it would make that much of a difference if you didn't.

     
  7. sabester24 macrumors member

    Joined:
    Jan 30, 2013
    #7
    So it doesn't matter which RAM goes into slots 1 & 3 vs 2 & 4?

    Mine is: Stock 4GB, Crucial 8GB, Stock 4GB, Crucial 8GB.

    I'm just trying to figure out why one would rearrange their stock RAM and not just put any additional RAM in the open slots.
     
  8. FreemanW macrumors 6502

    Joined:
    Sep 10, 2012
    Location:
    The Real Northern California
    #8
    Never having been a code monkey or a circuit designing electrical engineer or physicist . . . . I can only speculate that one of the paradigms at play here is a carry-over from the olden days of placing the higher capacity memory modules in the memory slot(s) closest to the CPU socket on the motherboard.

    Whether or not that survives today's contemporary circuit architecture? I have no idea. But there's no reason not to pair the larger capacity SODIMM's in the DIMM0 slots and to pair the lower capacity SODIMM's in the DIMM1 slots

    The other consideration remains utterly true and valid, that being, you want your memory modules paired so as to facilitate the provision for "Dual Channel" operation.

    /that is all ;-)
     
  9. sabester24 macrumors member

    Joined:
    Jan 30, 2013
    #9
    Interesting...I'd like to know if this still applies. While it's not a huge deal to rearrange the RAM, I'd rather not if it makes no difference nowadays.
     
  10. Zmaran thread starter macrumors newbie

    Joined:
    Jul 19, 2011
    #10
    Thanks. :)
     
  11. Zmaran thread starter macrumors newbie

    Joined:
    Jul 19, 2011
    #11
    I see you've been a member since 2011 as well, and it's quite interesting that you too have an iMac 5k now. Looks like we're on the same boat for a while. I was using a MBP mid 2010 all this while.
     
  12. seetheforest, Dec 22, 2015
    Last edited: Dec 22, 2015

    seetheforest macrumors member

    Joined:
    Dec 24, 2010
    #12
    I don't know if I should make a separate post for this, but I'm looking at the same configuration and have a question about it. If I'm getting the Crucial Ballistix 16GB kit with a CL of 9, and the stock ram has a CL of 13, is it better for me to just run the Ballistix and remove the stock RAM, or is it better for me to use all the sticks that I have.

    Which will be better for my overall computing experience? Is the difference in latency in the RAM not a big deal, of not, then why spring for the Crucial Ballistix?

    No Stock: 8 - 0 - 8 - 0
    Stock: 8 - 4 - 8 - 4
     
  13. FreemanW macrumors 6502

    Joined:
    Sep 10, 2012
    Location:
    The Real Northern California
    #13
    Presuming both pairs run concurrently without issue, you would require a software diagnostic and clocking clocking routine to tell the difference. Taking the speed of electricity and applying that speed to distance traveled in "T", we are discussing nano-millimeters here. ;)
     
  14. mtbdudex, Dec 24, 2015
    Last edited: Dec 24, 2015

    mtbdudex macrumors 68000

    mtbdudex

    Joined:
    Aug 28, 2007
    Location:
    SE Michigan
    #14
    So I bought these
    http://www.amazon.com/gp/product/B00DSGLMSM
    went from this
    [​IMG]

    to this
    [​IMG]

    and the memory instructions here never said to put the bigger ones like you stated
    https://support.apple.com/en-us/HT201191

    I'm open to doing that, just wish Apple had include such tid-bits in their formal instructions
     
  15. FreemanW macrumors 6502

    Joined:
    Sep 10, 2012
    Location:
    The Real Northern California
    #15
    Apple likely does not address the issue, because, well, it likely doesn't matter a lick. ;)
     

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