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From my understanding, the newest apple computers boot Windows in EFI mode. Traditionally, Windows has seen the boot disk as an MBR partitioned disk. In fact, the boot disk (i.e. /dev/disk0) has aways been partitioned as a GPT disk. I would like confirm there has been a change.

To be specific, open a Command Prompt as an Administrator and enter the following:

diskpart
list disk
exit

Note: When entering the diskpart command, it can take a while before the first prompt appears. This is normal. Be patient, the DISKPART> prompt will appear.

What I am looking for a * in the Gpt column for Disk 0. If Disk 0 is seen as an GPT partitioned disk, then Windows has booted using the EFI boot method. Otherwise, Windows has booted using the legacy BIOS boot method. An example, using an older apple (iMac/20 inch/Mid 2007), is shown below:

Example of diskpart command

In the above illustration, Disk 0 is the internal hard disk partitioned as a GPT disk. To Windows it appears as an MBR partitioned disk, indicated by the absence of the * in the Gpt column. Disk 1 is a GPT partitioned USB thumb (flash) drive containing a single NTFS partition.

If you show a * in the Gpt column for Disk 0, could you report back the "model identifier" or "model/screen size/year" of your apple computer. It may also be useful to include the version of Windows and OS X you are using. Apple recommends a standard where there is one partition for OS X and a second Boot Camp partition for Windows. If you are using a nonstandard partitioning scheme, try to indicate how you differed.

  • Do you know a comprehensive partition/disk editor/disk info/system info tool which presents more informations than just a (gpt) star for Windows? – klanomath Oct 20 '15 at 13:13
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    @klanomath: gdisk works with windows, but I have never tried this version. The Windows graphical tool is call Disk Management. It can be launched various ways. See this link. Personally, I wrote my own windows command line tool to do a text dump of the GPT contents. – David Anderson Oct 20 '15 at 16:52
  • Is the command line tool you wrote available anywhere? I'm asking because I have a spare MacBook Air (mid 2013) at the moment and while trying to answer this question I realized that I had no problem to create more than 4 partitions without losing the ability to boot to Windows. My mbr is empty except the pmbr. And I need a tool to inspect that further. – klanomath Oct 20 '15 at 19:51
  • @klanomath: For whatever its worth, I posted the command line tools at sourceforge.net. – David Anderson Feb 23 '16 at 14:58
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If you install Windows with the Bootcamp Assistant from a standard Mac OS X system, Windows always will start from a PMBR/Hybrid MBR partition table embedded in the GUID partition table (Legacy MBR). MBR takes precedence in hybrid configuration even if a EFI boot might be possible.

If you use a non-Bootcamp Assistant EFI install method for Windows (e.g outlined here) Windows will boot in UEFI-mode (compatibility Windows 32bit/64bit) and you will find a * in the Gpt column for disk0.

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