mismatched and odd numbered memory upgrade?

Discussion in 'iMac' started by DoNoHarm, Feb 28, 2016.

  1. DoNoHarm macrumors 65816


    Oct 8, 2008
    Hey guys, I'm hoping to upgrade my RAM, but I don't want to get something unnecessarily. I currently have a 2015 iMac with 2x4GB sticks of ram. Can I get just one 8gb stick of ram and have this frankenstein config of 4+4+8+0GB in my memory bay without there being some performance hit?
  2. Adam552 macrumors 6502

    May 30, 2006
    Liverpool, UK.
    You can but there will be a slight performance hit (some people say around 10%), it would be more advisable to go with 4+4+4+4.
  3. throAU macrumors 603


    Feb 13, 2012
    Perth, Western Australia
    What he said. You can go mismatched but there WILL be a performance hit.

    Basically if you match memory modules in pairs, your Mac can access memory twice as fast as it can split memory access across both sticks at the same time. If you mis-match, it can't.

    If you can't stretch to 2x 8 GB modules, buy another 2x 4GB modules for a total of 16 that way, you'll get better performance.

    and if you do go 4+4+8+8, you may need to verify which slots "match" to ensure that you match across channels. Not sure if the iMac slots are colour coded or what, but on PCs basically you want the RAM in the white slots to match each other and the RAM in the black slots to match each other for example. If your mac came with the 4+4 from the factory, just filling the empty slots should do it.

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