Combining iMac RAM

Discussion in 'iMac' started by snapdragonx, Jul 9, 2013.

  1. snapdragonx macrumors regular

    Oct 31, 2012
    Hey guys,

    I get my new 27" iMac tomorrow (WOO!). It's coming with 8GB RAM, and I've purchased 2x 8GB sticks of Kingston RAM to put in it.

    Will I run into issues if I combine the 2x 4GB sticks that come with the iMac, and the RAM that I purchased myself?

    Thanks in advance
  2. snapdragonx thread starter macrumors regular

    Oct 31, 2012
  3. Chippy99 macrumors 6502a

    Apr 28, 2012
    Not sure if it's mentioned in that thread, but this is important:

    If you intend to add ram to the Apple memory already installed, you must buy 1600MHz CL11 ram.

    You might be tempted to buy something like Corsair Vengeance 1600MHz CL10 ram. CL10 is faster than CL11, so that will be OK, surely? Well no.

    The iMac will try to run all memory sticks at the lowest latency any of the sticks can run at. So it will run everything at CL10 if you install that ram. The Apple ram can only manage 1333MHz at CL10, so you will find all the memory runs at 1333MHz is you install CL10 ram.

    Clearly this is slower than running at 1600MHz, which is the normal speed.

    So you will be slowing your machine down (albeit slightly) if you install faster ram that the iMac ships with. Paradoxical I know, but there you go.

    CL11 ram is your only choice.
  4. drambuie macrumors 6502a

    Feb 16, 2010
    I installed two Kingston KVR16S11/8 DIMMs in my 2012 iMac, alongside the Apple 8GB, in January, for a total of 24GB, and it has been 100% stable. The RAM chips on my Kingston DIMMs are Hynix, as are the Apple OEM DIMM chips.
  5. snapdragonx thread starter macrumors regular

    Oct 31, 2012
    Thanks guys. I installed 2x 8GB Kingston DDR3 1600 CL11 sticks and everything is working perfectly.

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