Ram Q's for iMac (Retina 5K, 27-inch, Late 2015)

Discussion in 'iMac' started by nobodyhome, Apr 11, 2016.

  1. nobodyhome macrumors member

    Jul 2, 2008
    I could really use some advice since I'm totally unfamiliar with ram. So I've been looking around online and in the forums and was hoping somebody could clarify some things for me based on what I've read and found.
    1. Does 2133mhz DDR3 ram in an iMac instead of 1867MHz/1866MHz really work and are there any repercussions?
    2. Does the difference between the recommended 1867MHz/1866MHz and 2133MHz make a huge difference? I normally run multiple graphics software simultaneously and sometimes video editing too.
    3. Am I correct in understanding 32GB sticks for the iMac don't exist?
      I was having trouble finding it, but then again I know nothing about buying ram...
    4. The specs on the Apple page say the highest the iMac can go is 32GB, but what is the highest it can really take? 4 sticks of 16GB making it 64GB? Is 128GB even possible or am I looking at the wrong ram sticks?
    Basically, I'm trying to figure out the best way to optimize the ram in the iMac, but I think I've gotten myself confused.

    Some minor questions are:
    Which brands are more reliable?
    Which are the quietest? (I have crazy hearing and can hear electricity buzzing or something. My old computer's buzz drove me nuts)

    Any advice is greatly appreciated. Thank you in advance!
  2. BrianBaughn macrumors 603


    Feb 13, 2011
    Baltimore, Maryland
    That's a lot of questions for your unknown model iMac.

    Everymac.com will have the best info on your max RAM.
  3. nobodyhome thread starter macrumors member

    Jul 2, 2008
    I thought I listed the iMac model in the title of the thread, but if I missed some important information please let me know and I will do my best to include it. I'm not the most savvy with the new iMacs and am willing to correct any mistakes I make.

    I will also check out everymac.com and see what it says. I just heard people online saying something about the iMac being able to handle more than what Apple said it could. I was looking for more info on that and answers to my questions. Still looking for a bit more info as I'm still not clear on some things. Thank you all the same tho.
  4. Omni Geno macrumors regular

    Omni Geno

    Apr 8, 2005
    Los Angeles, CA, USA
    Hi Nobodyhome,

    In general, a company should recommend RAM that runs at the speed of the bus. If the bus is 1866MHz, I'm assuming the bus speed is also 1866MHz. In that case, RAM that runs at 2133MHz will not run faster than 1866MHz, because the bus would be the bottleneck, in that case. To your question about whether there will be any repercussions, technically, there shouldn't be, but in the past I and people I know have had mixed results trying to use RAM that has specs other than the recommended ones. So your mileage may vary.

    That said, there are resources that make it easy for you.
    1) Other World Computing, at www.macsales.com. Specifically for you: http://eshop.macsales.com/item/Other World Computing/1867DDR3S4GB/
    2) Crucial: http://www.crucial.com/usa/en/compa...imac-(retina-5k,-27-inch,-late-2015)-imac17,1

    OWC will sell you kits so that you can have 16x4=64GB of RAM, double what Apple will offer in a standard config. Apparently the most recent 27" Retina 5K iMac will support that, whereas previous ones didn't. I haven't seen any evidence that it will support 32GB DIMMs, though.

    I've known both OWC and Crucial RAM to be very reliable. I'm sure there are others out there, but those two have not let me down.

    Sorry, I can't comment on the quietness of the RAM :].

    Take care.
  5. loekf, Apr 11, 2016
    Last edited: Apr 11, 2016

    loekf macrumors 6502a


    Mar 23, 2015
    Nijmegen, The Netherlands
    Search this forum I woulds say. 1866 vs 2133 MHz has been discussed a lot here, incl. which brands to buy for memory expansion.

    If I have to write something:

    - Late 2014 iMacs are by default 1600 Mhz, but 1833 MHz has been reported to work.
    - Late 2015 iMacs are by default 1866 MHz. They can handle 2133 MHz, because Skylake/Broadwell can do so. But you won't get a 13% speed increase. Computers are more complex than that.
    - Max. memory is 32 GB for OSX. Can be 4 x 8 GB max. You can mix and match DIMM sizes, but make sure pairs are the same size. E.g. slot A = 4 GB, slot B = 4 GB, slot C = 8 GB, slot D = 8 GB.
    - Don't mix different manufacturers and speed grades (e.g. 1866 MHz and 2133 MHz)
  6. BrianBaughn macrumors 603


    Feb 13, 2011
    Baltimore, Maryland
    Sorry! Didn't see the big print. I am too young to read large print.

    No matter which version of that iMac you have it does look like it will work with 64GB RAM...twice what Apple officially supports. It's OWC (macsales.com) that everymac.com uses as a reference. Keep your old RAM in case of issues.
  7. boomvader macrumors newbie


    Nov 13, 2015
    Asheville, NC
    Max memory is NOT 32GB. I am typing this from my iMac that has 64GB from OWC... It's not an OS limitation, but rather a CPU and/or chipset limitation.
  8. nobodyhome thread starter macrumors member

    Jul 2, 2008
    Thank you everybody for all the replies! Loads of good information that pretty much answers my questions! I have a good idea of what to do and get now. (Also, being young myself I think eyes either need to be checked or consider another cause for not being able to read large, bold print. I mean that in a joking sense so please don't take offense.)

    Thanks again! ;)
  9. iRaynor SK macrumors 6502

    iRaynor SK

    Nov 15, 2014
    Banská Bystrica, Slovak Republic
    I purchased 2x8 GB kit from Macsales, will it work with built-in 2x4 GB RAM?

    iMac Retina 5K Late 2015
  10. MinEderPlayz macrumors 6502a


    Aug 3, 2013
    Hamburg, Germany
    I have come across several people on the forum claiming they have 24GB RAM, so I'm assuming that's possible
  11. fat jez macrumors 68000

    fat jez

    Jun 24, 2010
    Glasgow, UK
    It should, but it will run at the slowest speed settings of the two pairs. The 2015 27" model can go to 64GB.
  12. mpe macrumors 6502

    Sep 3, 2010
    Yes they do work and they work just fine.

    Memory intensive apps (compression) will run faster as the memory throughput is faster. The effect is to some extent negated by slightly increased latencies, but the memory performance is better. Also Apple stock modules are not particularly great so you almost always see some improvement. Graphics software/video editing is less likely to show major performance gains as they typically have different sort of bottlenecks than pure memory bandwidth. But tasks like compression could see improvement.

    I replaced the shipped 2x4GB 1833 MHz modules with 4x8GHz 2133 MHz and geekbench benchmark +23% in stream memory performance and about +3% across the board. It doesn't have any measurable effect on my productivity thought (apart from increased RAM capacity of course which has big impact on my tasks).


    I think 64GB is the max. I would be surprised if they ever make higher density modules in DDR3L factor. Vendors are switching production to DDR4.

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