Will my bootcamp partition be gone?

Discussion in 'macOS' started by Cudadown, Feb 27, 2009.

  1. Cudadown macrumors regular

    Dec 14, 2007
    Hey all....
    Right now I have 2 partitions on my iMac. One 260gig for OSX and the rest for vista (must have fallout 3 & FSX). Bootcamp works great as is. I would like to be able to install another version of OSX onto a small (40gig) partition to play around with it. When I go into disk management to create the new partition taking the needed space from the main OSX partition area, it tells me my bootcamp partition may become unbootable if I proceed. Is this true? I though on macs we could always shift around partitions with relative safety. I'm not wanting to change the size of the windows partition. Im just stealing some from OSX side.
  2. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    Yes, I believe it is true; though I don't know what the details are, Bootcamp does something special when it creates its partitions that is different from however Disk Utility creates partitions. I've got experience with this because when setting up some new machines I partitioned the drives before installing OSX, then discovered that I couldn't get Windows to install properly onto the partition I reserved for it--I needed to destroy that partition and let Bootcamp make a new one.

    Now, it's possible that so long as Disk Utility is dividing the existing HFS+ partition and leaving the Bootcamp one alone you'll be ok, but I assume it's going to mess with the partition map, which will in turn probably break the bootability of Windows. It's possible that iPartition or the like can do this without messing up the partition map, but I wouldn't be optimistic, and it's not free, either.
  3. larkost macrumors 6502a

    Oct 13, 2007
    Unfortunately, this is going to be a little tricky to do because of the way the "legacy boot" section of EFI works. So you are probably going to have to do a bit more work to get this to work after you change partitioning. I have spent a lot of time working on this, so can give you some notes off the top of my head:
    • The windows partition has to be in the first 4 partitions on a disk to fit on the (faked) MBR (Master Boot Record) that Apple puts on, and it has to be the last one on MBR (which is limited to 4 slots). This gets little complicated because there is a EFI partition on all disks that takes the first slot that gives you three slots that you can use. You started with 2 user partitions: (EFI +) MacOS + Windows. And now are switching to 2: (EFI +) MacOS + MacOS + Windows.
    • You need to make sure that the MBR is correct for your new partition scheme, and that sure that the appropriate partition is marked in MBR as the one bootable option (in MBR). There are some weird details about the cylinder counts that you have to make sure are right (or more accurately: get a tool to do for you)
    • Make sure that you tell MacOS X that your Windows partition is bootable (it does not pay attention to the MBR at all).
    • For Windows XP you need to make sure that the BOOT.INI file on the Windows partition points to the right partition number. The Windows installer probably did this for you the first time, but it can't correct it for you. Vista has a whole new system, and I can't help you there.

    The best tool for the job is probably 'gptrefresh', a part of the WinClone project. You can dig it out of the WinClone.app bundle (in Contents/Resources).

    Executive summary: this is not an easy thing as it stands in 10.5.

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