Right after Internet Recovery finished installing OS X Mavericks (10.9.5) on my Late 2013 27-inch iMac, I run Boot Camp Assistant. A window pops up with this message:

The startup disk cannot be partitioned or restored to a single partition. The startup disk must be formatted as a single Mac OS Extended (Journaled) volume or already partitioned by Boot Camp Assistant for installing Windows.

While I'm 100% sure about it, I run Disk Utility again and see that the entire 3TB space of my ST3000DM001 disk is allocated to a single, Mac OS Extended (Journaled) partition.

So I google that message and find HT209102 which tells me to:

  • Install the latest macOS updates -> Done (there were no updates actually)
  • Use Disk Utility to repair the startup disk -> Done. No errors found.
  • Check for unallocated free space -> Done. No unallocated free space.

I still see that message and can't proceed with Boot Camp. What I'm supposed to do now?

  • Which version of Windows did you intent to install? Have you considered installing a a version of OS X (macOS) that is newer than Mavericks? Dec 12, 2021 at 13:55
  • I've not reached the stage to install Windows because I have to create a partition for that first and it's not possible because of that message. Also, you can't decide which version of OS X to install. The recovery determines that based on the model. Dec 12, 2021 at 14:51
  • Open a Terminal application window and enter the command diskutil list. Edit your question and post the output from this command. This will show any hidden partitions that may not appear in the Disk Utility windows. Dec 13, 2021 at 21:14

1 Answer 1


Upgrade to a newer version of OS X or macOS before trying to use the Boot Camp Assistant to install Windows to your Mac. What I mean by Windows is the latest version of Windows 10 available, which can be downloaded as an ISO file from this Microsoft website. To keep using Windows 10 after installing, you will need to a license, which may require a purchase. You may still be able to license by using the product key from a previous version of Windows.

The newest version of macOS that Apple states is compatible with your Mac is Catalina. However, this requires using APFS, which will probably have poor performance when installed to the internal HDD. High Sierra is the last version of macOS that does not require APFS, so you should probably at least upgrade to this version. The instructions for downloading the upgrade software application is given here. If you have problems getting High Sierra, then try for Sierra.

If after upgrading to a newer version of macOS, the Boot Camp Assistant will not allow the installation of Windows 10, then you should still be able to make the Windows 10 installation flash drive. Post a comment and I will update this answer to include instructions to finish the installation of Windows 10 without further use of the Boot Camp Assistant.

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