Yosemite on new Skylake 27" iMacs?

Discussion in 'iMac' started by RubberShoes, Nov 19, 2015.

  1. RubberShoes macrumors regular

    Jun 30, 2007
    Hey guys (and gals)

    I am wondering if anyone knows if you can downgrade the new late-2015, Skylake-based 27" iMacs down to Yosemite. This is for compatibility reasons in our existing office infrastructure and El Cap's new rootless features really screw up some custom stuff for us. Right now we have 2013 non-retina macs that came with Yosemite and we were successfully able to downgrade them to Mavericks back in the day. But I believe those iMacs came out before Yosemite so the hardware always supported Mavericks.

    Anyone with one of these machines or knowledge on the subject can you confirm?

    Thanks guys,
  2. ivoruest macrumors 6502


    Jul 12, 2010
    Is it possible for you to perform a backup and do a hard restore?
  3. UbuntuFu, Nov 19, 2015
    Last edited: Nov 19, 2015

    UbuntuFu macrumors regular

    Aug 16, 2007
    You would probably need to download a copy of Yosemite and put it on a USB stick, boot and completely wipe the hard drive in order to install it on the new Skylake iMacs.

    It's likely that Yosemite will support the latest generation iMac in terms of driver support but I can't confirm that.

    The more thought I gave it, it may not work since these iMacs came out after El Capitan was released.
  4. DamnDJ macrumors regular


    Feb 17, 2003
    Denver, CO
    It has always been my understanding that you cannot install an OS older than the one shipped with the machine.
  5. BornAgainMac macrumors 603


    Feb 4, 2004
    Florida Resident
    Try VMWare for running a older Mac OS on it.
  6. maflynn Moderator


    Staff Member

    May 3, 2009
    No because the older OS does not have the kexts needed for the newer chipset. Apple does not allow you to downgrade to a lower version of the OS then what was shipped with it.

    As noted above, you could run Yosemite in a VM if needed for a specific app or task.
  7. redheeler macrumors 604


    Oct 17, 2014
    No, Yosemite has no support for Skylake. However, you can disable rootless/System Integrity Protection in the El Capitan Recovery partition: boot the iMacs holding down Command-R, Utilities > Terminal and run csrutil disable.
  8. RubberShoes thread starter macrumors regular

    Jun 30, 2007
    To close this out, Skylake and Broadwell require the new kexts so nope, El Cap it is. The previous iMacs we received we were able to downgrade because the model was announced with Mavericks so even though it came with Yosemite Mavericks had the necessary kexts.

    Thanks for your responses!
  9. MrNomNoms macrumors 65816

    Jan 25, 2011
    Wellington, New Zealand
    The solution to your custom set is to update the code, sign the kexts etc. One day you're going to have to update your custom in house software to work properly so you might as well do it now before it becomes a lot more painful later on.

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8 November 19, 2015