EFI system partition

src: oi64.tinypic.com

EFI system partition ( ESP ) is a partition on a data storage device (usually a hard disk drive or solid-state drive) used by computers that follow the Unified Extensible Firmware Interface (UEFI). When the computer is booted, UEFI loads firmware files stored in ESP to start installing the operating system and various utilities.

ESP contains a boot loader or kernel image for all installed operating systems (contained in other partitions), device driver files for hardware devices that are in the computer and used by the firmware at boot time, the system utility program intended to be run before the system boot operation, and data files like error logs.

Video EFI system partition

Ikhtisar

EFI system partitions need to be formatted with file systems whose specifications are based on the FAT file system and are maintained as part of the UEFI specification; therefore, the file system specification does not depend on the original FAT specification. The unique global identifier (GUID) for the EFI system partition in the GUID Partition Table (GPT) scheme is C12A7328-F81F-11D2-BA4B-00A0C93EC93B , while the ID in the master boot record (MBR) of the partition-table scheme is 0xEF . Partitioned GPT and MBR disks can contain EFI system partitions, because UEFI firmware is required to support both partitioning schemes. Also, El Torito's bootable format for CD-ROM and DVD is supported.

UEFI provides backward compatibility with legacy systems by ordering the first block (sector) of the partition for compatibility code, effectively creating the old boot sector. On a legacy BIOS-based system, the first sector of the partition is loaded into memory and execution is transferred to this code. UEFI firmware does not execute code in MBR, except when booting in legacy BIOS mode via Compatibility Support Module (CSM).

The UEFI specification requires the MBR partition table to be fully supported. However, some UEFI implementations immediately switched to BIOS-based CSM booting when it detected a particular partition table type on the boot disk, effectively preventing UEFI booting from an EFI system partition located on an MBR-partitioned disk.

UEFI firmware supports booting from removable storage devices such as USB flash drives. Therefore, removable devices must be formatted with FAT12, FAT16 or FAT32 file systems, while the boot loader must be stored in accordance with standard ESP file hierarchies, or by providing a full boot loader path to the boot manager system.

Maps EFI system partition

Usage

Linux

GRUB 2 and elilo serve as a standalone UEFI standalone boot manager for Linux. Once loaded by UEFI firmware, both can access and boot kernel images of all devices, partitions and file systems they support, without being restricted to EFI system partitions.

EFI Boot Stub makes it possible to boot Linux kernel image without using a conventional UEFI boot loader. By masquerading as a PE/COFF image and appearing into the firmware as a UEFI app, the x86 kernel image with EFI Boot Stub enabled can be directly loaded and run by UEFI firmware. The kernel image can still be loaded and run by a BIOS-based boot loader; thus, EFI Boot Stub enables a single kernel image to work in any boot environment.

Linux kernel support for EFI Boot Stub is enabled by enabling the option CONFIG_EFI_STUB (EFI stub support) during kernel configuration. It was merged into version 3.3 of the main Linux kernel kernel, released on March 18, 2012. Gummiboot (a.k.a. systemd-boot) is a simple UEFI boot manager that loads and runs a configured UEFI image, accessing only EFI system partitions. Configuration file fragments, kernel images and initrd images are required to be on the EFI system partition, because Gummiboot does not provide support for accessing files on other partitions or file systems. The Linux kernel needs to be built with CONFIG_EFI_STUB enabled so they can be run as UEFI images immediately.

The mount point for an EFI system partition is usually /boot/efi , where the contents are accessible after Linux is booted.

Mactel

On Mactel computers based on x64, the EFI system partition was initially empty and not used to boot. However, EFI system partitions are used as staging areas for firmware updates.

The system will still boot after the EFI partition is deleted, in which case the boot manager will allow the user to choose whether to start the default Boot Camp or Mac OS X partition, but firmware updates will fail.

Windows

Microsoft recommends that when partitioning the disk, the EFI system partition becomes the first partition on the disk. This is not the EFI specification requirement itself. On Windows XP 64-Bit Edition and later, access to the EFI system partition is obtained by running the mountvol/s command.

ESP drivers can be temporarily created if your Windows system is waiting for a restart after Windows Update. This is to allow the computer to start up in the Windows Update environment (Mini OS) so there are no competing apps during the update. This drive, and the appropriate space, must be restored to the host drive (actual physical drive) after the completion of the update.

TrueOS (BSD operating system)

TrueOS 'UEFI support (only for amd64) has been added to the installer and boot manager since version 10.1 with the default EFI boot manager for rEFInd. This includes ACPI detection and Root System Description Pointer (RSDP) settings, XXT System Descriptor Table (XSDT), and Root System Table Set (RSDT) set values ​​to the kernel. A new installation is required to install UEFI support as it requires the creation of a small FAT partition. UEFI does not currently support secure boot.

src: www.minitool.com

See also

• BIOS boot partition
• EFI variable
• System partition and boot partition
• Windows To Go

src: www.datanumen.com

References

src: i2.wp.com

External links

• EFI System Partition Subdirectory Registry - List of subdirectories located under the /EFI directory on the EFI system partition

Source of the article : Wikipedia