I have read many posts regarding installing and booting Windows on Mac computers. Many procedures use rEFInd to boot a BIOS install of Windows. The procedures do not seem to indicate any installation of code in the MBR. So either the assumption is there is already code in the MBR from a previous install or rEFInd does not require such code to boot Windows. Does anyone know the answer?
Answer
Both rEFIt and rEFInd will place a copy of SYSLINUX MBR boot code in the MBR if the MBR is not already bootable and if appropriate boot code exists in a partition. That said, boot code should exist in the MBR, although it might be destroyed by partitioning tools that assume the first 440 bytes of the MBR on a GPT disk should be zeroed out, as is normally the case for EFI-bootable GPT disks.
This brings up another point, though: Windows 8 (and presumably Windows 10) installs pretty well in EFI mode on many Macs. When installed in this way, no BIOS-mode boot code is necessary, in either the MBR or in the Windows partition(s). An EFI-mode installation is likely to be safer because there's no need for the dangerous hybrid MBR that Macs use to dual-boot OS X and earlier versions of Windows. The catch to this type of installation is that Disk Utility and some other OS X tools will create a hybrid MBR if you try to prepare the disk for Windows -- for instance, by setting up a FAT partition. When the Windows installer, booted in EFI mode, sees the hybrid MBR, it will complain that it can't install to an MBR disk. You can work around this problem by using any number of tools (such as gdisk: Type x, then n, then w), but it can be frustrating and confusing if you don't understand the nature of the problem or how to fix it.
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