UEFI

File Format
Name	UEFI
Ontology	Electronic File Formats Firmware UEFI
Extension(s)	(none), .bin, .efi

Please do not delete/format your EFI System Partition, you may not be able to boot back into your OS if you do so.

UEFI (Unified Extensible Firmware Interface) is a specification and code that replaces BIOS in the boot ROM. Many modern devices, particularly those with 64bit x86 CPU or ARM SoC (System on a Chip), have UEFI.

Typically, machines with UEFI and are booted with UEFI enabled, would have a partition on the storage medium known as ESP (EFI System Partition). This partition is formatted as FAT32 as per UEFI specifications, and all UEFI compliant operating systems would have their EFI files stored in the same partition. Other tell-tale signs involve (but are not limited to):

• System configuration screen or system manual describing the likes of CSM (Compatibility Support Module), Secure Boot, a mouse driven interface^*,
• Use of GPT (GUID Partition Table) as opposed to MBR (Master Boot Record)^*2,
• (In Linux mainly), /sys/firmware/efi/efivars is present and accessible for instance.

^*: Exceptions to this rule may apply to older machines, usually with AMIBIOS (American Megatrends Inc BIOS), which may have a mouse driven interface.

^*2: This is likely not part of UEFI specification, it is possible to have UEFI on MBR.

UEFI compliant OS takes advantage of sharing ESP, thereby eliminating the need to worry about bootloaders being overwritten by another OS, especially if dual-booting or multi-booting. For example, Microsoft Windows is known to typically overwrite MBR with its own bootloader, and this would prevent Linux from being booted. Backing MBR (on BIOS only machines) were tricky, but even with UEFI, it is still recommended to backup your ESP to prevent rendering the loss of your OS choice.

Extensions as noted in the infobox is not an exhaustive list of possible extensions that exists within the ESP. As previously stated UEFI is a specification, therefore hardware vendors are free to place whatever files as they like. For instance, on ARM powered devices, they may contain .dtb (Device Tree Binary).. Dell machines may also place the likes of .rcv (BIOS recovery file) inside ESP.

Software

• efibootmgr (Linux only) - Allows viewing and manipulation of entries in /boot/efi or /boot/esp
• UEFITool - Viewer and editor of firmware images conforming to UEFI Platform Interface (PI) Specifications.

Links

• wikipedia:UEFI
• How to extract system specific data from UEFI BIOS? (MAC address, SN, UUID, MSDM key, etc.) - Stack Exchange
• tianocore - community supporting an open source implementation of the Unified Extensible Firmware Interface (UEFI)