EFI system partition

When a computer is booted, UEFI firmware loads files stored on the ESP to start operating systems and various utilities.

The actual extent of divergence is unknown:[2][3] Apple maintains a separate tool that should be used on Intel/x86-64 Macs,[4] while other systems use FAT utilities just fine.

UEFI firmware does not execute the code in the MBR, except when booting in legacy BIOS mode through the Compatibility Support Module (CSM).

[12] On Apple Mac computers using Intel x86-64 processor architecture, the EFI system partition is initially left blank and unused for booting into macOS.

[14][16] Custom Apple UEFI firmware named iBoot controls the logic for finding and loading bootloaders.

iBoot will select the desired bootloader (potentially configured via Startup Keyboard Combinations or NVRAM), optionally falling back to either the internal macOS Installation, or a recovery system called recoveryOS.

There are otherwise no limitations to what kinds of EFI operating system or bootloader an Intel-based Apple computer can run.

[18][19] Devices using Apple silicon (AArch64) such as iPhones, iPads and all Mac computers from 2023 onward do not contain EFI/UEFI functionality and subsequently do not use EFI system partitions.

[23] On Windows XP 64-Bit Edition and later, access to the EFI system partition is obtained by running the mountvol command.