iMac 27" late 2013 RAM slot question

Discussion in 'iMac' started by in4fun, Sep 28, 2013.

  1. in4fun macrumors regular

    Dec 4, 2012
    So I want 16GB with my new iMac.

    By default, 8 GB is installed as two 4 GB memory modules (and two slots are unoccupied).

    Does it make sense to add another 2x4 GB memory modules to have 16 GB total and all slots occupied (4x4GB)


    should I rip out the existing 2x4 GB and buy 2x8 GB to get 16 GB total?

    Beside the costs are there any negative effects regarding processing speed etc?

    I guess it's also not a good idea to mix brands - what are the original ram units, samsung?
  2. bluescale macrumors member

    Sep 27, 2013
    You should buy 16GB (2x8) and add it without ripping out the 8GB in there. The machine runs beautifully with 24 GB of RAM. My friend did that with the late 2012 iMac he got in Feb, and I'm planning to do that with this one that will come next week.

    Mixing RAM brands isn't a huge deal, as long as the RAM is high quality, and has the same specs. Crucial has great quality RAM. For whatever reason, Crucial's iMac RAM is $30 cheaper on Amazon than through their website. That's where I just ordered my 16GB from earlier this morning.
  3. in4fun thread starter macrumors regular

    Dec 4, 2012
    ok, thanks bluescale - 24 is even better :cool:

    does anyone know the exact specs, something like 'PC3-10600 1333MHZ CL9'?


    Ah I just found it

    PC3-10600 DDR3 1600 MHz CL9

    and I read CL9 is very important

    ...the brands are Samsung and Hynix, no one can foresee which one you actually get
  4. Bear, Sep 28, 2013
    Last edited: Sep 28, 2013

    Bear macrumors G3

    Jul 23, 2002
    Sol III - Terra
    Matching the CL is indeed important, buy it's actually CL11. I do recommend you make sure your iMac works fine before adding the memory you buy. The brand is not important as long as you buy reputable memory.
  5. in4fun thread starter macrumors regular

    Dec 4, 2012
    thanks a lot

    I also read you loose dual channel capability but that it's not noticeable in everyday use
  6. bluescale macrumors member

    Sep 27, 2013
    Where did you see CL9? I'm pretty sure it's CL11:


    I should clarify, you can use CL9 RAM if you want, as long as the bus speed is the same. However, you won't see any noticeable difference, and I thought iMacs shipped stock with CL11 anyway.
  7. Bear macrumors G3

    Jul 23, 2002
    Sol III - Terra
    The dual channel capability is by pairs of memory modules.. you just need to make sure that each pair is in the right slots.
  8. Giuly, Sep 28, 2013
    Last edited: Nov 23, 2014

    Giuly macrumors 68040


    Here's the conundrum: Haswell also runs 1866MHz memory, and a 2x8GB 1866MHz Kingston HyperX Plug'n'Play SODIMM kit exists, too.

    So, on top of black (ripping 2x4GB out and installing 2x8GB) and white (installing them alongside for 24GB), I also present you some shades of gray here: Installing 16GB 1866MHz RAM alongside the old RAM and running both at 1600MHz, or ripping the 8GB RAM out and running the 16GB at 1866MHz.

    The answer is 42. Err, 24. No matter what, leave the old 8GB RAM installed and enjoy 24GB.

    But if the slightest possibility exists that you - at some point in time - want to upgrade to 32GB, go with the 1866MHz. Even if it downclocks to 1600MHz when installed along the old RAM, it'll work at full speed when you install a second kit.

    Otherwise, a 16GB 1600MHz Crucial kit will serve you well - exactly the same specifications as stock RAM, and the most inexpensive of the premium RAM.
  9. in4fun thread starter macrumors regular

    Dec 4, 2012

    sorry, of course it's CL11 not CL9


    thanks for the tip
    I found the crucial ram and it has the following specs

    16GB kit ( 8GB x 2 )
    204-pin SODIMM
    DDR3 PC3-12800 , CL=11 , Unbuffered , NON-ECC , DDR3-1600MHz , 1.35V

    I can get it for €130 ( 8GB €80) so I guess it's a fair deal.

    also thanks for the tip regarding 32 GB but I hope that 24 GB will serve me just fine for the next 4-5 years
  10. bluescale macrumors member

    Sep 27, 2013
    Does the 2013 iMac bus run at 1866MHz? I'm pretty sure it's a 1600 MHz bus. Your RAM should match your bus speed.


    You can get it a bit cheaper on Amazon :)

    Make sure I got the specs right, as I just glanced at it, but I'm pretty sure this is the same stuff.
  11. in4fun thread starter macrumors regular

    Dec 4, 2012
    that is the amazon price in germany :D
  12. Giuly, Sep 28, 2013
    Last edited: Sep 28, 2013

    Giuly macrumors 68040


    Eventhough they don't have a real bus anymore: Theoretically yes, practically most Macs that are stated by Intel as DDR3-1066/1333 work fine with 1600MHz (some even work with the 1866MHz HyperX kit above) memory, too. Kicking it up one notch worked on they majority of Macs until now, and it should still work on Haswell.

    Especially the iMac, as those Haswell desktop CPUs even run fine on 2166+MHz RAM.
  13. Old Muley macrumors 6502a

    Old Muley

    Jan 6, 2009
    Titletown USA
    I found these on the US Amazon site. Price looks good to me.
  14. bluescale macrumors member

    Sep 27, 2013
    Interesting. I didn't know that. Aside from benchmarking, however, is there any real world benefit of 1866 vs. 1600?

    That's what I just ordered, and it should work flawlessly.

    I'm interested in what Giuly has to say, and if he/she can convince me that 1866MHz RAM is the way to go, since the RAM won't ship until Monday. I can always cancel my order and go with the more expensive 1866MHz if there will be an appreciable difference.
  15. alksion macrumors 68000


    Sep 10, 2010
    Los Angeles County
    Short answer, no. Are there certain applications that may benefit, perhaps, but only marginally.
  16. TwoBytes macrumors 68030


    Jun 2, 2008
    Won't faster ram speed lead to system instability/crashes?
  17. MrGimper macrumors 603


    Sep 22, 2012
    Andover, UK
    If you pair faster RAM with slower RAM, the faster drops to the speed of the slower.
  18. bimmeracer macrumors regular

    Oct 13, 2008
    I always thought that all of the rams sticks should match. Can mixing and matching cause any potential problems?
  19. lefty224 macrumors member

    Sep 20, 2013

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