Now that Windows 8 is officially supported in the latest BootCamp, I am considering this for my Mac.

There is plenty of general advice about installing Windows 8 / Windows 8 Pro in BootCamp on a Mac.

However, what I do not see is how to clean install a Windows 8 Pro upgrade on a mac with an existing BootCamp Windows 7 install. Clean install is an option offered in the upgrade install process for general PCs - but can this work on BootCamp?

Why do I want to install Windows 8 Pro upgrade ?

Because it's much cheaper than the regular version (though it is still a full OS install) and I am eligible in that I already have a legal licensed copy of one of the pre-requisite operating systems to qualify - I have Windows 7 64bit installed in bootcamp on my mac. In other words Microsoft offer Windows 8 cheaper if you have a legal copy of an earlier qualifying OS.

What do I mean by Windows 8 Pro clean install?

I also have a desktop PC which used to run Windows 7. I clean installed the Windows 8 Pro upgrade on this successfully. Although Windows 8 Pro upgrade is a full OS installation, during the install process, it will check the hard disk for the presence of a valid, licensed eligible OS already installed - in my case Windows 7. BUT, once its done that, it offers the option to format the disk on which it is to be installed. Obviously I would have backed up any valuable files, deactivated any applications and uninstalled them -ready to reinstall and reactivate them on the new OS later. A fresh start. I prefer the clean install approach as to me this is the optimal deployment; no baggage/kruft/residue/ditritus/call it what you will from a prior OS. I also hear anecdotally from friends that an "in-place" upgrade whereby Windows 8 retains personal files and apps during install has proved unreliable for them.

So can anyone advise me about clean installing Windows 8 Pro upgrade on Bootcamp that already had Windows 7 installed?

(By the way, I would not want comments or discussion about why I should have Windows/Windows 8 on my Mac. Not useful to me. I work in computing and prefer to keep a balanced informed opinion of what is out there to help me and others. Thanks!)

4 Answers 4


It should be possible to do the clean install of a Windows 8 Pro upgrade on an existing installation of an earlier qualifying OS as these steps for Windows 7 suggest:


In this guide above, search for string: "Theoretically, you're doing a fresh installation of Windows 7. In that case, select the "Custom (advanced)" installation"

(remove just the outermost quotes when searching for the string in the guide.)

In summary, after the Mac BootCamp app has done its original setup (including the partitioning), the rest of the setup is as per usual Windows installation - all the Windows steps are shown. In the event of the usual ReBoots, be sure to select the Windows drive to continue the installation.

During the install, once the Windows 8 upgrade installer has found the previous qualifying OS on the disc, it can then offer the format disc as the clean installation option.


Not sure if it helps, but I have done 2 installs of windows 8 pro upgrade, wiping the existing OS in the process without issue on windows computers. The existing OS was a trial version of the latest windows home server, I forget what its called. So, Windows 8 for the cost of an upgrade. Per one of the answers above, you have the option of completely wiping the existing OS. The upgrade should verify suitability to upgrade prior to commencing the upgrade process. I can't see why this wouldn't work on a mac with bootcamp. I will give it a go myself this weekend on my MBP.

  • +1 upvote @Bruce Comrie I would agree as most of the install process is standard Windows. Commented Apr 12, 2013 at 8:44

For me, an upgrade isn't clean, so I recommand you to format the ntfs partition, resize the osx partition to max and renew the bootcamp operation.

Otherwise you can use vmware to use bootcamp partition as virtual machine ;-)

  • -1 downvote @clement if you read my question properly you would see that a) the windows 8 / windows 8 pro upgrade edition DOES offer to format the disk after it has checked that you have a previous OS that the upgrade is relevant and b) following your instructions would remove this previous OS and the upgrade would not be able to find it and proceed. Please re-read my question. Moreover your answer appears to be subjective: "for me..." - what do you mean by that? In any case, a format option in the upgrade install process is offered which would make it clean. Commented Mar 15, 2013 at 14:26

There is a big difference between a "clean install" and an "upgrade install". A clean install of windows 8 on your mac wipes your exiting (window 7 PARTITION completely clean, aka empty) PRIOR to installing windows 8, whereas an upgrade install over-writes the windows 7 partition, and "may" leave a ton of windows 7 unused files on the partition that "may or may not" cause a problem later with the new OS, so a clean install is always recommended, - but "no good deed goes unpunished". IF you do a "CLEAN install" with a legal windows 8 UPGRADE OS, as it loads, it asks for your new windows 8 "key/license" and proceed with installing windows 8. After about 90 minutes of installation comes the problem. The installer looks to your partition for the previous windows 7 "key/license". It ain't there - you cleaned out the partition of all data. To use the technical term - your screwed !!!!!!! No windows 8 - no windows 7. To do a clean install windows 8 with the new bootcamp "8 drivers" you must have a new "FULL - retail or full - OEM" windows 8 with new key/license. If not you can only do an upgrade install. You can use the newest bootcamp app to do either install.

  • -1 Downvote: This answer is poor quality as it does not cite references to back up the statements it is making. Commented Mar 17, 2013 at 22:08
  • For example: "upgrade install over-writes the windows 7 partition, and "may" leave a ton of windows 7 unused files on the partition that "may or may not" cause a problem later with the new OS" Upgrade install actually has two options: 1. is an in-place upgrade which retains apps and programs from the existing installation present on disk and this is not the option I am interested in as explained in the question. The second option allows the disk to be formatted - which provides the route for the clean install upgrade. Commented Mar 17, 2013 at 22:11
  • Even a quick format which removes the listing of the files in the directory ought to be sufficient, as the incoming OS to be installed won't be aware of the remains of these files. Commented Mar 17, 2013 at 22:12

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