The EFI System partition is a partition on a data storage device

Data storage device

thumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....

 that is used by machines that adhere to the Extensible Firmware Interface

Extensible Firmware Interface

The Unified Extensible Firmware Interface is a specification that defines a software interface between an operating system and platform firmware...

. It contains the boot loader programs for all operating systems installed (in other partitions) on the device, device driver files (used by the firmware

Firmware

In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...

 at boot time) for other devices, and system utility programs that are intended to be run before an operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 is booted.

The EFI System Partition is formatted using a variant of the FAT

File Allocation Table

File Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...

 format. The Globally Unique Identifier

Globally Unique Identifier

A globally unique identifier is a unique reference number used as an identifier in computer software. The term GUID also is used for Microsoft's implementation of the Universally unique identifier standard....

 for the EFI System Partition in the GUID Partition Table

GUID Partition Table

In computer hardware, GUID Partition Table is a standard for the layout of the partition table on a physical hard disk. Although it forms a part of the Extensible Firmware Interface standard , it is also used on some BIOS systems because of the limitations of MBR partition tables, which restrict...

 scheme is C12A7328-F81F-11D2-BA4B-00A0C93EC93B. Its ID in the MBR Partition Table

Master boot record

A master boot record is a type of boot sector popularized by the IBM Personal Computer. It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk...

 scheme is 0xEF. Whether a disk contains an EFI System Partition is unrelated to the partition table scheme (GUID or MBR) that it uses.

Windows

Microsoft recommends that when partitioning a disk, the EFI System Partition be the first partition on the disk. This is not a requirement of the EFI specification itself. On Windows XP

Windows XP

Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...

 and later, access to the EFI System Partition is obtained by running the mountvol /s command.

Apple–Intel

On Apple–Intel architecture Macintosh

Macintosh

The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

 computers, the EFI partition is initially blank and not used for booting. However, the EFI partition is used as a staging area for firmware updates; specifically, it places a firmware flash utility (EFI binary) and data file (FD – "Firmware Device") in the directory EFI/APPLE/FIRMWARE which is then run when rebooting the system in "flash firmware" mode.

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

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

, but firmware updates will fail.

External links

— a registry of the subdirectories that lie below the /EFI directory on an EFI System Partition