Downgrading iMac 27" to Yosemite

Discussion in 'OS X Yosemite (10.10)' started by kaejouge, Oct 10, 2017.

  1. kaejouge macrumors newbie

    Oct 10, 2017
    Hey all, I've just bought a new iMac (Retina 5K, 27-inch, 2017) and I need to downgrade an install Yosemite on it

    I can't find any instructions on how to do that...

    As far as I know I need to downgrade the EFI, but I can't find any related

    Hope there's some help out there
  2. Significant1 macrumors 6502

    Dec 20, 2014
    AFAIK you can't run earlier versions of macOS than the version preinstalled when your model introduced. They simply lack drivers for the newer hardware. Yosemite is from October 2014, while your iMac generation is from mid 2017.

    You could run it in a virtual machine, but I wonder why you want to run an old and since september unsupported version of macOS..
  3. chrfr macrumors 604

    Jul 11, 2009
    Like the post above says, this is not possible. What are you using that requires Yosemite?
  4. kaejouge thread starter macrumors newbie

    Oct 10, 2017
    We’re using a custom system made for yosemite and it does not work with newer OS - told them several times to upgrade, but nothing happens...

    @Significant1 thanks, Will try to set up a virtual machine

  5. jbarley macrumors 68040


    Jul 1, 2006
    Vancouver Island
    If you really needed Yosemite, maybe a good used 2014 iMac would have filled the bill.
  6. kaejouge thread starter macrumors newbie

    Oct 10, 2017
    Yeah, I’ve got one already, but who would ever say no to a new one :)
  7. PaulRanger2 macrumors newbie


    Nov 9, 2015
    I also bought a new iMac 21.5" 2.3GHz Retina 5k recently. I need to install Yosemite or find a workaround as I have non Apple software (e.g. Photosop Elements 8, Streamclip Version 1.9.3b8 (1.9.3b8) -open source creators no longer support program- among others) that El Capitan and later OS X versions will not recognise or distort the software features unacceptably. I cannot purchase commercial alternatives to Streamclip, thus presenting an apparent impasse.

    From an external drive (Mac OS Extended [Journaled] formatted, I attempted to install Yosemite OS X 10.10, onto a newly created partition on the new iMac's HD, from the Apple "Install Yosemite" installer. A warning said that OS X version was too old to be installed.

    Can anyone please suggest a workaround solution to this dilemma as I need to use these software programs.
  8. Significant1 macrumors 6502

    Dec 20, 2014
    Run it in a virtual machine is one way, maybe the only way.

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