EFI can be compatible with legacy booting, but on Windows PCs, the firmware is set to tell EFI to boot in Legacy mode to an MBR disk. Windows had a very different way of booting, based on a Master Boot Record (MBR), sometimes refered to this as “Legacy Booting”. When Boot Camp was introduced to the Mac, Windows XP was all the rage. The boot loader was located on the HFS+ volume in /System/Library/CoreServices.

The EFI partition did not contain the boot loader for Mac OS X. After the EFI partition was a HFS+ partition that contained Mac OS X. The specification for EFI requires an EFI partition at the start of the disk, and Apple-partitioned disks had a 200 MB empty EFI partition. Earlier builds of the original version of Mac OS X could boot on FDisk partitioned disks, but past those earlier builds, GPT was the partition scheme that all Intel-based Macs started with. Intel-based Macs are different from PPC-based Macs, as they used EFI to boot the operating system. When Mac OS X was introduced, the partition scheme was the GUID Partition Table, or GPT.

I’ll then discuss how this affects High Sierra and finally some guesses on where this is all leading.

How does this affect Boot Camp? Let’s dive in a bit and look at the progression of partitioning changes since Boot Camp was introduced. APFS is not just a filesystem to replace HFS+, but also replaces Core Storage as the volume manager. MacOS 10.13 High Sierra has now been released, and one of the major features is a new filesystem called APFS. Posted on Septemby Timothy Perfitt - Uncategorized

Boot camp mac os sierra