I'm trying to install Windows 7 on my MBA, 2010.

I open up Boot Camp and attempt to use it, but after the first screen it comes up with an error saying it can't install unless theirs 10GB of free disk space. Right now my HDD has 21.5 GB free. Disk Utility won't let me partition my drive either, so a manual install is out of the question.

I need help! My original thoughts were that my disk needed to be defragged to get 10GB of contiguous space. Is this a possibility?

  • Macs don't need to be defragmented, so it wouldn't help.
    – Dori
    Feb 2, 2011 at 7:29
  • @Dori Yeah I know Macs don't need to be defraged but that's only for files under 20MB. At one point my HDD was down to 100MB free, so I could have large files spread all over the hard drive. Feb 2, 2011 at 7:31
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    Did you tried to repair the HD in Disk Utility and attempt using Bootcamp utility again?
    – balexandre
    Feb 2, 2011 at 7:45
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    Please do not crosspost. Feb 2, 2011 at 8:36
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    With only 64GB of HDD space, I would advocate to not install Windows. You wouldn't even have space to properly use Windows in about 10GB (most installs start at about 18GB, maybe it can squeeze down, I am not sure). For instance, downloading and installing updates would require additional space, not to mention the applications you wish to run on the Windows side. Feb 2, 2011 at 22:58

3 Answers 3


Unfortunately the solution is not a great one.

I had a similar problem on my MacBook a while ago, and the problem is actually due to file fragmentation, however no defrag tool could actually solve the problem. There are various solutions on Google indicating that a defrag does work, but I had no success with any of them.

The problem is related to how the files are spread on the drive, and BootCamp requires a continues 10GB or more of free space on the drive to be able to create the required partition.

The only way I got around the problem eventually was to format and reinstall the drive.

My honest advice is to look at using something like VirtualBox which is free, and create a virtual image for Windows. Depending on what you need to do, you can get away with a relatively small image. Windows 7 can run quite happily with only a 1GB of RAM if you don't need Aero. You can also look at paid for options like Parallels or VMWare Fusion

Alternatively, you could look at installing Windows on a secondary drive via USB. The speed won't be great, but if again, depending on what you need it for, it might be a sufficient solution.

  • What can you tell me about installing Windows on a USB drive? Can I use a flash drive or does it have to be a hard drive? This seems like the best solution because VirtualBox won't work with the myDAQ I need to use Windows with. I thought of a USB drive before but dismissed it because I thought Mac OS X couldn't boot from USB flash drives. Thanks for the quick answer! Feb 2, 2011 at 8:34
  • @SeniorShizzle Unfortunately you'll need to do some research on that, however OSX will happily boot from a USB drive as long as it has an EFI boot sector. I would suggest booting from the Windows 7 DVD and seeing if it will allow you to select an external USB drive to install on. I would suggest an HDD because it would have a better chance of being detected. Feb 2, 2011 at 8:40
  • Windows does not permit installing on a flash drive or external device of any kind. It can only be installed on internal HDDs. Of course you can have the virtual machine files anywhere, including USB devices. Feb 2, 2011 at 22:52
  • Which defrag tools did you try?
    – alimack
    May 15, 2015 at 12:30

To expand upon my above comment:

64GB is just not very much space, especially when you consider updates, your own programs, data, etc etc.

My recommendation, if it is possible and available, is to run Windows XP from a USB drive. There are a handful of documented procedures for getting WinXP on a flash drive and running it from there. I would recommend following this TechRepublic article to get it all set up for that.

This should negate the issue with Boot Camp, let you keep the 64GB of HDD space to your trusty OS X partition, and hopefully provide enough room on your flash drive for WinXP to grow with applications as well.

Hopefully there is nothing Vista or Win 7 specific that you need to do. Good luck!


MacOSX has a defragmenting utility that is run in the background when your Mac is idling. It's possible that the "Free Space" being shown in Disk Utility is not accounting for any swap space that the Hard Drive uses. If you are down to about ~20GB of free space, it's probably not enough free space for the Disk Utility to move all of the essential files it needs to move in one piece to fit a new partition in that new space. I might also mention that even if you were to be able to get fit a 10GB partition into that ~20GB of free space, you would only have about ~10GB of free space left on your hard drive which is probably getting close to the point where your system slows down enormously because there isn't enough space on the hard drive to do all of the tasks it needs to do with moving files, file swap, etc.

My best advice would be to use a utility like GrandPerspective (http://grandperspectiv.sourceforge.net/) which basically shows you a picture of all the 'stuff' on your hard drive and might give you an idea of some files that you can get rid of and what might be eating up a lot of space.

  • Yeah I use DaisyDisk on a daily basis it seems. At one point I had 100MB free TOTAL. My MBA has a 64GB hard drive. The system occupies about 20GB of that with it's OS and various libraries and stuff, so that's like 44GB free, then -10GB for Xcode and SDKs, then -5GB for Photoshop, Illustrator, Word, iWork Suite, and Aperture. That means I have only used about 8 GB total for all my other applications and files. That's pretty good seeing as my graphic art files are often hundreds of MBs or even a few GBs. These are my job, so without these things my system is completely worthless to me......... Feb 2, 2011 at 8:25
  • ......But I did think about the SWAP file, like you said. But it shouldn't be 10GB. I looked at it with DaisyDisk and the file is around 3GB, which is instantly deleted if the space is needed. As far as defragmentation goes, Mac OS X will only automatically defragment files under 20MB, which is something that surprised me when I learned it because I originally had the same thought as you. I also don't think that having 10GB free will slow my computer. The MBA has Flash memory, not a regular HDD, so it's not affected by that phenomenon, at least it wasn't when I only had 100MB free. Feb 2, 2011 at 8:29
  • Okay... Well as you have probably noticed 64GB isn't much of space these days. It's fast when it comes to being an SSD but flash storage takes up more volume per bit. If it's absolutely imperative that you can run Windows, maybe you might want to look into getting an external hard drive and using something like Parallels to create a virtual machine on that external hard drive, or storing the stuff you don't necessarily need on the main drive on the external drive.
    – liltechdude
    Feb 2, 2011 at 8:30

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