How to install Windows 8.1 on a Mac

By uliwitness

WindowsOnMac

Update: Microsoft now sells Windows 10 on USB keys, so even Mac users can install it easily if they order physical media. Also, I’ve heard (but have been unable to confirm) that Microsoft’s download version of Windows now can be obtained as an .ISO disk image again, which the Mac’s Disk Utility can extract onto a USB key.
 
I’m leaving this article up for people who somehow still end up with the .exe installer and are looking for a workaround.

It is not quite trivial to buy Windows as a download and get it onto your Mac. I’ve found a workaround, but it takes a lot of time, and requires you to download about 7GB of data via the internet.

Disclaimer: I do not guarantee that these steps will work. They worked for me in late June 2015, YMMV. Do not blame me if you buy a download version of Windows and then can’t install it. Also, be sure to make a backup of your entire hard disk/SSD before you do this. You will be resizing partitions and doing other things that could lead to accidental loss of data.

The Problem:

  • The microsoftstore.com Windows 8 download is a small .exe file containing a downloader application that needs an already-installed Windows to work.
  • Macs these days don’t have a DVD drive, so you’d need to buy/borrow one to be able to use install DVDs mailed to you.
  • Boot Camp Assistant assumes a physical DVD or an ISO disk image, it obviously can’t run the .exe under MacOS.
  • I was unable to get the .exe downloader to run under CrossOver on MacOS.

My workaround:

  • Download the trial of Windows 8.1 for Enterprise as an ISO image from Microsoft (need to create an MS account which you will also later need to buy the download)
  • Use Boot Camp Assistant to install that onto an empty USB stick that is at least 4GB (not just the Apple-specific drivers, check the option for the full install partition). The stick will be formatted using Windows’ old FAT32 format, which both Mac and Windows can read and write.
  • ~100GB (at least 60) is a good size for the Windows partition to add to your internal hard disk/SSD.
  • Boot Camp will now churn a while and copy the files from the ISO on your USB stick, and will also download the newest hardware drivers from Apple and make sure those get installed as well. Time for breakfast.
  • When Boot Camp Assistant reboots, hold down the option key and select the “EFI Boot” entry to make sure you don’t end up back in MacOS.
  • You will find yourself in the standard Windows installer now. Follow its directions. On Retina Macs, it will be at a tiny 1:1 resolution. Bring a magnifying glass.
  • When asked where to install the Boot Camp partition, find the one named “BOOTCAMP” and select it. Remember what else it says (e.g. “Disk 1 Partition 4”).
  • If the Windows installer complains about the partition not being formatted as NTFS, Click the “Format” button underneath the list, but don’t do any repartitioning with the Windows tools, you’d only disturb the fairy dust that Boot Camp Assistant has applied and break booting back into MacOS.
  • Select the reformatted disk (which has now lost its “Bootcamp” name) and click “Next” to start installing the trial.
  • Make lunch while pretty colorful screens rotate through and Windows is set up for you in the background.
  • Run through the Boot Camp installer that runs in Windows after the standard Windows installer has finished.
  • Once you have a working trial install of Windows, buy the download .exe from microsoftstore.com, if you haven’t already. Unless they say they don’t, installers include both old-style 32-bit versions and the 64-bit versions needed for Macs, don’t worry.
  • Run the .exe you just bought while you’re running the Enterprise Windows Trial to create a proper ISO with your purchased Windows 8.1 on it.
  • Back up that Windows.iso and its license key somewhere safe.
  • Copy the Windows.iso onto the USB stick so you can get at it from MacOS.
  • Note down the Windows license key somewhere, you’ll need to type it in in a moment.
  • Boot back into MacOS and run Boot Camp Assistant a second time to remove the trial partition. (BCA doesn’t let you run it again on an existing partition, so you’ll have to nuke and recreate)
  • Run Boot Camp Assistant a 3rd time, this time using the new ISO, not the trial, to get the desired full Windows install. Remember to hold down the Alt key at startup to select “EFI Boot” or you’ll just end up back in MacOS.
  • When the standard Windows installer comes up, you’ll need to enter your Windows license key this time. From then on, the install will be identical to the trial install.
  • Your Yak is shaven clean as a baby’s bum.

Note: In theory, it should be possible to run the .exe under the trial to directly install Windows 8.1 on top of the trial instead of generating the ISO, but I didn’t want to risk it somehow generating a mix of the trial and purchased Windows installs, or eliminating the Boot Camp-supplied drivers & programs, so I decided to nuke the trial once I had the ISO and start fresh. Whatever you do, generate and back up the ISO so you don’t need to request another trial from MS when you inevitably want to reinstall Windows at a later time, even if you then use the .exe and not Boot Camp for the second installation.

Thanks:Thanks to Sören for pointing me at the Windows trial version that made this possible.

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