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What I understand is that Windows 7 will not install on GPT (GUID Partition Table) drives. Of course, all new Macs have their drives partitioned that way, and when you run the boot camp assistant, it is taking advantage of the GPT to resize your main partition on the fly and free up some space for the Windows installer to create an NTFS (or whatever) partition.

Of course, it doesn't wipe out your disk and repartition with MBR (Master Boot Record) since all of your data is intact at the end. So, I think the assistant is adding an MBR alongside the GPT, or creating some kind of hybrid partition table?

Second: It's easy enough to use Disk Utility to resize your main partition and leave free space. Is it possible to "manually" do whatever else Boot Camp Assistant is doing to prep the drive for Windows?

Context: Mid-2010 iMac Core i5, Mac OS X 10.7.4, Boot Camp 4.0.3, Windows 7.

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@JeremyW You know, I thought I had it right by tagging with [mac] instead of [osx] since I'm dealing with sub-OS hardware and partition tables. On the other hand, I'm also asking about Disk Utility which is a component of the OS... but what it's doing to the drive is OS-independant. –  NReilingh Jun 3 '12 at 1:47
    
As I understand it UEFI and GPT are not limited to mac hardware. Bios support is required but that isn't limited to macs either. If your question is (how do I make software do .... so that I can install Windows) then I don't think [mac] helps but as you're the author, if you want to re-add the [mac] tag, I understand. –  Jeremy W Jun 3 '12 at 2:59
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1 Answer

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Boot Camp Assistant creates a hybrid partition table. The GPT that is present by default is synced to a MBR.

MBR partition tables can only handle up to four partitions, so anything beyond that in your GPT will not be synced.

Disk Utility cannot do this, but rEFIt's gptsync will.

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