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 bootedEFI specification, version 0.99.

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 disc contains an EFI System Partition is unrelated to the partition table scheme (GUID or MBR) that it uses.

Microsoft recommends that when partitioning a disc, the EFI System Partition be the first partition on the disc. This is not a requirement of the EFI specification itself. On Windows XP and later, access to the EFI System Partition is obtained by running the mountvol /s command.

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