Boot Camp shenanigans

Windows logoApple’s new Boot Camp Assistant pulls a neat trick: if you have a single Mac OS X partition on your startup drive – it allows you to non-destructively repartition it and add a partition to install Windows XP.

But what if you’ve already partitioned your drive? Boot Camp Assistant refuses to run and tells you you must have a single partition. Do you really need to reformat to play with Apple’s new toy?


I’ve since installed XP on a MacBook Pro that had already been set up with three partitions without having to repartition. Here’s how I did it:

1) Started up the MacBook Pro in Target Disk Mode.
2) Connected it via FireWire to an Intel iMac.
3) Used Disk Utility (on the Intel iMac) to reformat one of the unused partitions as FAT32
4) Unmounted the MacBook Pro and shut it down
5) Booted the MacBook Pro and held down the option key, and inserted the XP install CD.
6) The XP install CD showed up in the boot picker; I selected it and booted from it.
7) Installed XP as normal.

I imagine that steps 1 and 2 could be replaced with booting from the OS X install CD – the key is that you can’t reformat a partition to a different disk format on the startup disk when you are booted from it, since the entire disk must be unmounted. I haven’t tested this theory (yet).

Boot Camp shenanigans

10 thoughts on “Boot Camp shenanigans

  1. Nigel Kersten says:

    Did you have to do anything special with the partition table Greg? I’ve been unable to get Win XP to see my FAT32 partition unless I choose “MBR” rather than GPT in Disk Utility’s options… which doesn’t seem ideal…

  2. Nope. I have a GPT disk wih two ~30G HFS+ partitions and a ~30G FAT32 partition (The FAT32 partiton was converted from HFS+). When I first got the MacBook Pro about three weeks ago, I partitioned it into three equal-sized HFS+ partitions. I didn’t want to have to reformat to install Windows, and I ended up not having to. Something I left out of my description above which may or may not be relevant: I originally tried to use Disk Utility to restore a disk image of a WinXP install on an Intel iMac to the FAT32 partition, but then couldn’t get the MacBook Pro to boot from it, so I then started up from the WinXP CD, erased the partition, and installed again. I still think it will be possible to restore disk images ala Ghost, but haven’t had time to work on it again.

  3. Hmm. Maybe it’s the conversion that did it. I’ve been partitioning with a FAT32 partition directly and it’s not working properly.

    I experimented with making a single HFS+ partition, doing things the bootcamp way, then resizing the HFS+ partition down to make a new HFS+ partition, but that killed the Windows install that I did via BootCamp.

  4. So I worked out what I’d been doing wrong.

    1) The Windows partition needs to be the last one, the setup process never completes otherwise. I imagine you can probably get around this by modifying boot.ini, but it’s not seamless.

    2) Choosing MS-DOS file system in Disk Utility seems to not do the same thing as using diskutil from the command line, to make an “MS-DOS FAT32” partition.

    3) according to the triple boot instructions at, the hard drive needs to be dual GPT/MBR, but I can’t work out how to tell if this is the case. According to diskutil, I’ve got a GPT disk, but I guess it’s possible there’s some MBR thing going on somewhere…

  5. So I probably just lucked out – I had three partitions and reformatted the last partition as the FAT32 one, and it worked. The triple boot info at is interesting – I wonder what a hybrid MBR/GPT partition scheme actually *is*…

  6. So after messing around with getting Ubuntu onto an Intel Mac here… I’ve worked out what this hybrid stuff is.

    OS X actually keeps a mirror of the GPT partition tables around in MBR format, and that’s why it is a ‘hybrid’. If you use diskutil to partition, this is all hunky dory (so long as it is a recent enough version of diskutil…).

    If you partition using parted or some other GPT aware partitioning tool, you’ll have to look at something like rEFIt (It’s at sourceforge), as it can re-sync the MBR side to the GPT partition table.

  7. arun says:


    I have a different problem. Not sure if some one can help me.

    I have 4 partitions in total. 3 of which are “Journaled HFS+” and other is “MSDOS FAT32”.

    On my 3 mac partitions, i have 10.4.7, 10.4.6 and 10.4.4.

    I have erased the data on “MSDOS FAT32” because i wanted to subdivide it.

    my “MSDOS FAT32” is of 40G, and i want to split it into two “MSDOS FAT32” drives of 20G each.

    The problem is Diskutility (diskutil) does not support partitioning “MSDOS FAT32” drive.

    How do i Create two partitions of “MSDOS FAT32” without altering my mac drives…

    Any ideas?

    PLEASE POST ME on my email id –

    Thanks a lot in advance.

  8. Kelsey Wildstone says:

    Greg and Nigel, Thanks a bunch for the info, It is really helpful. I was wondering myself if using disk util to format a FAT partition would make the disk a hybrid, so it’s encouraging to hear you guys say it does. Thanks again!

  9. Rodney Fawcett says:

    I bought a 160 GB Fuji Harddrive on line and it is GT Parted and I need to reformat it into NFTS format to run it on my dell 1501 Inspirion. The seller claimed it to work on a dell laptop 2.5 SATA. Is their a work around or utility that will let me do it on a dell. I would apreciate any help I could get Thank you in advance.

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