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OK. Right now I have a perfectly working dual boot laptop with Ubuntu 12.10 and Microsoft Windows 8 (both in UEFI mode). The disk is partitioned in GPT format (needed by Windows UEFI installation and preferred by me).

What I would like now is to enable a function of the laptop (called ExpressGate) that allows me to boot an different OS from a special button. The function works finding an special file in a FAT/NTFS partition in a MBR disk, and I know that works with hybrid disk.

But it's impossible to me to make Windows boot from a hybrid partition (using the gdisk tool).

Someone had any ideas?

Daniel Otero
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Windows ties its boot mode to its disk type. It boots in EFI mode only from GPT disks, and it boots in BIOS mode only from MBR disks. Windows also sees hybrid MBR disks as being MBR disks, whereas Linux and OS X see such disks as being GPT disks. This is why hybrid MBRs are useful to Apple: They enable a Mac, which uses GPT for OS X, to also boot Windows using the Mac firmware's BIOS emulation mode and a hybrid MBR.

Using a hybrid MBR on a PC can also work, but then you'd need to boot Windows in BIOS mode. An in-place conversion is theoretically possible, but is likely to be awkward to enable. I don't have a step-by-step procedure handy, nor do I have a reference to one. Switching between BIOS mode and EFI mode booting on most PCs is also awkward. Furthermore, hybrid MBRs are ugly and dangerous hacks. I do not recommend their use unless they're absolutely required. (Note that I'm the author of gdisk, so I know a thing or two about them. I've just answered a question on this site from a user who trashed his disk because of a hybrid MBR.)

Overall, I'd say that you're best off either giving up on this idea or converting your whole setup to boot in BIOS mode using an MBR setup on your disk.

Rod Smith
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