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The EFI System partition (ESP) is a partition on a data storage device (usually a hard disk drive or solid-state drive) that is used by computers adhering to the Unified Extensible Firmware Interface (UEFI). When a computer is powered up and booted, UEFI firmware loads files stored on the ESP to start installed operating systems and various utilities. An ESP needs to be formatted with a file system whose specification is based on the FAT file system and maintained as part of the UEFI specification; therefore, the file system specification is independent from the original FAT specification. ESP contains the boot loader programs for all installed operating systems (which are contained in other partitions on the same or any other local storage device), device driver files for hardware devices present in a computer and used by the firmware at boot time, system utility programs that are intended to be run before an operating system is booted, and data files such as error logs. ==Overview== The EFI System partition needs to be formatted with a file system whose specification is maintained as part of the UEFI specification; the file system itself is based on the FAT file system but is independent from the original FAT specification.〔 The globally unique identifier (GUID) for the EFI System partition in the GUID Partition Table (GPT) scheme is , while its ID in the MBR partition table scheme is . Both GPT- and MBR-partitioned disks can contain an EFI System partition, as UEFI firmware is required to support both partitioning schemes. Also, El Torito bootable format for CD-ROMs and DVDs is supported.〔 UEFI provides backward compatibility with legacy systems by reserving the first block (sector) of the partition for compatibility code, effectively creating a legacy boot sector. On legacy BIOS-based systems, the first sector of a partition is loaded into memory and execution is transferred to this code. UEFI firmware does not execute the code in the Master Boot Record (MBR), except when booting in legacy BIOS mode through the Compatibility Support Module (CSM).〔 The UEFI specification requires MBR partition tables to be fully supported.〔 However, some UEFI implementations immediately switch to the BIOS-based CSM booting upon detecting certain types of partition table on the boot disk, effectively preventing UEFI booting to be performed from EFI System partitions contained on MBR-partitioned disks. UEFI firmware supports booting from removable storage devices such as USB flash drives. For that purpose, a removable device needs to be formatted with a FAT12, FAT16 or FAT32 file system, while a boot loader needs to be stored according to the standard ESP file hierarchy, or by providing a complete path of a boot loader to the system's boot manager.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「EFI System partition」の詳細全文を読む スポンサード リンク
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