The EFI System partition is a partition on a data storage device that is used by machines that adhere to the Extensible Firmware Interface. It contains the boot loader programs for all operating systems installed (in other partitions) on the device, device driver files (used by the firmware at boot time) for other devices, and system utility programs that are intended to be run before an operating system is booted.[1]
The EFI System Partition is formatted using a variant of the FAT format. The Globally Unique Identifier for the EFI System Partition in the GUID Partition Table scheme is C12A7328-F81F-11D2-BA4B-00A0C93EC93B. Its ID in the MBR Partition Table scheme is 0xEF. Whether a disk contains an EFI System Partition is unrelated to the partition table scheme (GUID or MBR) that it uses.
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Microsoft recommends that when partitioning a disk, the EFI System Partition be the first partition on the disk.[2] This is not a requirement of the EFI specification itself. On Windows XP 64-Bit Edition and later, access to the EFI System Partition is obtained by running the mountvol /s command.
On Apple–Intel architecture Macintosh computers, the EFI partition is initially blank and not used for booting.[3] However, the EFI partition is used as a staging area for firmware updates;[4] specifically, it places a firmware flash utility (EFI binary) and data file (FD – "Firmware Device"[5]) in the directory EFI/APPLE/FIRMWARE which is then run when rebooting the system in "flash firmware" mode.[6]
If deleted, the system will still boot, and the boot manager will still allow users to choose whether to start a Boot Camp partition or the default Mac OS X, but firmware updates will fail.
/EFI directory on an EFI System Partition