if you are adding memory with the exsiting memory, the speed is 2133MHZ

Discussion in 'iMac' started by robertchen117, Jun 23, 2017.

  1. robertchen117 macrumors newbie

    robertchen117

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    Jun 23, 2017
    #1
    if you are adding memory with the exsiting memory, the speed is 2133MHZ instead of 2400MHZ, for 2017 imac 27',

    which is very strange...???
     
  2. trsblader macrumors 6502

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    #2
    Are you sure the ram you added was the correct speed? What does it say if you take the apple ram out and use only your newly bought ram? I've seen quite a few screenshots in the couple other ram threads for the 2017 iMacs and they say 2400.
     
  3. EugW macrumors 68000

    EugW

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    Jun 18, 2017
    #3
    Get properly spec'd RAM specific for the iMac and it will be 2400 Hz.

    [​IMG]

    You've encountered a common problem when you get third party RAM that is not specifically listed as compatible with Macs.
     
  4. keysofanxiety macrumors 604

    keysofanxiety

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    #4
    Nah. RAM is RAM, though obviously get a decent brand like Crucial and make sure the sockets/speeds are correct. RAM listed as "Mac compatible" just means it's the right RAM for that machine to avoid confusion for the end user, rather than being officially sanctioned by Apple or something.
     
  5. Brazilano macrumors newbie

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  6. Gjwilly macrumors 68030

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    #6
    The latency is just as important and that's where a lot of problems happen with Macs.
    Right socket, right speed, wrong latency equals :(
     
  7. robertchen117 thread starter macrumors newbie

    robertchen117

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    #7
  8. Glideslope macrumors 601

    Glideslope

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    #8
    Also needs to be listed as Lead and Halogen Free. :apple:
     
  9. SaSaSushi macrumors 68040

    SaSaSushi

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    #9
    This is apparently a known issue with the Kingston HyperX. See this thread.
     
  10. EugW macrumors 68000

    EugW

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    #10
    Yup. Even if you get RAM that is over spec'd, it may not be fully compatible. Sure, it could be run slower and running under spec but that doesn't matter. Apple expects very specific parameters, and if it doesn't get them, you may run into problems, like the original poster has now discovered.

    Sorry to tell you, but you bought the wrong RAM.

    Wrong CAS latency listed and it probably doesn't identify itself as being compatible with Apple's expected latency.

    The RAM you bought is actually over-spec but that doesn't matter, as it isn't fully Mac compatible.
     
  11. trsblader macrumors 6502

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    #11
    Specifically this part

    "I should note the computer shows 2133MHz when looking at the memory in the "about system" under the apple menu. Not sure if it does that with the factory RAM as well. The chips clearly state 2133-2666MHz so I'm not concerned.

    Read the data sheet for the Kingston RAM. It's overclocked. It lays out specific conditions for the RAM to run at 2400, and it sounds like the iMac does not meet those conditions. You should return it immediately."
     
  12. robertchen117 thread starter macrumors newbie

    robertchen117

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    #12
    what is the CAS latency for this kingston hyperx? So I should return it?
     
  13. SaSaSushi macrumors 68040

    SaSaSushi

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    #13
    Thank you for confirming this.
     
  14. robertchen117 thread starter macrumors newbie

    robertchen117

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  15. EugW macrumors 68000

    EugW

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    #15
    If you want to use all your 48 GB RAM, then return the 32 GB Kingston RAM and buy other RAM. Your RAM is CL14. Apple uses slower CL17 RAM I believe.
     
  16. SaSaSushi, Jun 23, 2017
    Last edited: Jun 23, 2017

    SaSaSushi macrumors 68040

    SaSaSushi

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    #16
    I do not believe the problem with the Kingston is the CAS Latency. The problem is that it is actually 2133MHz RAM overclocked to 2400MHz.

    If it were me, I would definitely return the Kingston and get actual (non-overclocked) 2400MHz DIMMs.
     
  17. robertchen117 thread starter macrumors newbie

    robertchen117

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  18. EugW macrumors 68000

    EugW

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    #18
    The RAM I bought was Crucial. See above pic. It was actually cheaper than most of the enthusiast RAM but I know I won't run into compatibility issues. I don't like buying store brand RAM like OWC because I'm not really sure what I'm getting.

    I think Crucial.com is sold out, but bhphoto had some recently.
     
  19. Gjwilly macrumors 68030

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    #19
    Yep.
    OWC and Crucial both agree. CL17 for that iMac.
     
  20. SaSaSushi macrumors 68040

    SaSaSushi

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    #20
    Again, the biggest problem with the Kingston HyperX is that it is actually an overclocked 2133MHz part. The iMac will run it overclocked when it is installed on its own but not when paired with actual 2400MHz RAM like the stock memory.

    I installed 2x16GB Crucial Ballistix (2400MHz) CL16 RAM in addition to the Apple Stock RAM and 40GB is running perfectly, all at 2400MHz. I assume it is running at CL17, the slightly slower speed of the Apple RAM.

    I also recommend getting Crucial, but don't worry as much about the CAS latency as the frequency.
     
  21. EugW macrumors 68000

    EugW

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    #21
    Not sure how it works these days, but in the past some RAM would self-identify as being compatible with various RAM timings, etc. regardless of what was written on the paper label stuck to it.

    ie. You could buy DDR1600 CLx that ran fine at DDR1333 CLy even on machine that only booted if the RAM specifically stated it needed DDR1333 CLy. Why? Because the RAM would identify itself as being compatible with DDR1333 CLy and DDR1600 CLx.

    Then if you bought competing DDR1600 CLx RAM of the same quality but which didn't have the alternate timings, etc. listed, it simply would not boot.

    I wonder if the Crucial Ballistix is more thorough in listing its compatible timings.
     
  22. SaSaSushi macrumors 68040

    SaSaSushi

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    #22
    To reiterate my point, CL is not as important as the RAM frequency (2400MHz) when adding memory to the iMac. If you add good quality (e.g. Crucial) PC4-19200 2400MHz (non-overclocked) RAM with a faster CL, it will just run at the slower CL17 speed of the stock Apple RAM.

    This is why the frequency is specified but there is no mention of CL at the memory upgrade pages for the iMac at the Apple website.
     
  23. EugW macrumors 68000

    EugW

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    #23
    It is always the case now? Because that wasn't always the case in the past.
     
  24. robertchen117 thread starter macrumors newbie

    robertchen117

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    Jun 23, 2017
    #24
    Not sure about crucial, I used a lot crucial SSD disks before, the ssd disks did have more fault rate than other brands.
     
  25. SaSaSushi, Jun 23, 2017
    Last edited: Jun 23, 2017

    SaSaSushi macrumors 68040

    SaSaSushi

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    #25
    This was my experience for this Mac as well as the Late 2013 which preceded it.

    I can't speak for Crucial's flash drives. Personally, I am partial to Samsung.

    Apple themselves use Crucial RAM along with other makers like Hynix and Samsung.

    I have always had good experiences with Crucial RAM.
     

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