RAM shows up as 1600 MHz instead of 1866?

Discussion in 'iMac' started by johannnn, May 30, 2017.

  1. johannnn macrumors 65816

    johannnn

    Joined:
    Nov 20, 2009
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    Sweden
    #1
    Newly purchased Late 2015 iMac. Put in "Corsair Mac Memory - DDR3L - 16 GB: 2 x 8 GB - SO DIMM 204-pin - 1866 MHz / PC3L-14900 - CL11 - 1.35 V" that was branded as "Apple memory". Forgot to look in "About this Mac" before the RAM update, but looking now it says that all my four RAM slots have 1600 MHz memory. Does macOS often misrepresent RAM speed, or should I worry? I know 1600 vs 1866 is not a big difference in terms of speed, but I still want to obtain 1866 speeds if that's what I have.
     
  2. DeltaMac macrumors 604

    DeltaMac

    Joined:
    Jul 30, 2003
    Location:
    Delaware
    #2
    Check the speed WITHOUT the Corsair memory installed?
    Then, replace the original sticks with the pair from Corsair (so that's the only installed memory), and check the reported speed again.
    If you want to be sure about the RAM that you purchase, get it from a vendor that is well-known for Mac support, such as Crucial, or Data Memory Systems.
     
  3. rybitronn macrumors newbie

    rybitronn

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    Celina, TX
    #3
    Perform a PRAM reset and see if that has any affect.
     
  4. nambuccaheadsau macrumors 6502a

    nambuccaheadsau

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    #4
    You used the wrong memory and the 1867MHz module/s are being throttled back to the slowest speed.

    Further check out what you have actually purchased as the mid 2015 models did use 1600MHz memory, not 1867MHz. If this is a 27" model, the late 2015 is known as the 17.1 model iMac, the mid 2015 as the 15.1 iMac.
     
  5. hurtmemore, May 30, 2017
    Last edited: May 30, 2017

    hurtmemore macrumors member

    Joined:
    Jan 9, 2017
    #5
    Technically the iMac is rated for 1867 mhz. I've heard 1866 should work and register as 1867 - but normally if you use slower ram, everything downclocks to the next spec which is 1600 mhz. So it's possible that's what's happening, maybe it's registering as 1866, not 1867, and then dropping all the way down to 1600. Question is why, when others have success with 1866mhz chips.

    You said you got PC3L-14900 memory - Apple's specs say it's just PC3 in an iMac. The 'L' is a lower-voltage model, compatable but I suspect this is keeping it from registering at the full 1867mhz. Bit of info here. https://www.quora.com/Can-I-use-a-PC3-RAM-with-existing-PC3L-RAM
     
  6. drambuie macrumors 6502a

    Joined:
    Feb 16, 2010
    #6
    If you have RAM of different speeds installed, the system will default to the lowest speed RAM. In your case, you mixed 1600MHz and 1866MHz RAM therefore the system defaulted to 1600MHz.
     
  7. johannnn thread starter macrumors 65816

    johannnn

    Joined:
    Nov 20, 2009
    Location:
    Sweden
    #7
    Thanks for all responses.

    I actually removed the end of the description for the ram, the entire description is "Corsair Mac Memory - DDR3L - 16 GB: 2 x 8 GB - SO DIMM 204-pin - 1866 MHz / PC3L-14900 - CL11 - 1.35 V - not buffered - not ECC - for Apple iMac with Retina 5K display (Late 2015)", so it's really weird if this memory doesn't have the same speed as the iMac memory.

    The computer is indeed Late 2015 (17.1 model).

    I agree removing either the built-in or the purchased memory would be an easy test to see which of them register as 1600MHz. The only problem is, I actually find it Very hard to remove the memory now when all four slots are taken. There is just no room for my big fingers since the slots are so close to each other!
     
  8. nambuccaheadsau macrumors 6502a

    nambuccaheadsau

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    Nambucca Heads Australia
    #8
    Sounds like you need a plastic 'spudgee' to remove the memory.

    Just leave it be I have not seen bench tests on the various memory sizes, but for mine I think it would not be greatly noticeable.
     
  9. RyanXM macrumors newbie

    RyanXM

    Joined:
    Jul 7, 2012
    Location:
    DFW, TX
    #9
    Did you try a PRAM Reset? https://support.apple.com/en-us/HT204063

    This is a known issue in the Mac Pro 5,1 when you upgrade to the Xeon 5600 Series and upgraded the RAM to the 1333 spec. They would run at 1066 until you did a PRAM reset and then they would run at the full 1333.
     
  10. nambuccaheadsau macrumors 6502a

    nambuccaheadsau

    Joined:
    Oct 19, 2007
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    #10
    He did not try to convert a Mac Pro 4.1 to a 5.1.

    This is an iMac.
     
  11. RyanXM macrumors newbie

    RyanXM

    Joined:
    Jul 7, 2012
    Location:
    DFW, TX
    #11
    I know this....I'm simply saying that as an ACMT, this can resolve this issue.
     

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