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Definition: UEFI

(Unified Extensible Firmware Interface) A standard programming interface for booting a computer. Governed by the UEFI Forum (www.uefi.org), it evolved from the EFI interface developed by Intel, first used in its Itanium line. Designed to replace the BIOS startup system, UEFI is also compatible with older BIOS-based machines.

PCs began shipping with UEFI in the mid-2000s, and Microsoft support began with the 64-bit versions of Windows Vista and Server 2008. Most Windows, Mac and Linux machines support UEFI, but all of its features may not be supported in all versions. For example, UEFI's secure boot, which prevents malware from infecting the code, did not appear in Windows until Windows 8 (see secure boot).

UEFI Is Software Based
UEFI resides in a folder in flash memory on the motherboard, storage drive or network drive. The U in UEFI (Unified) means any platform can be supported by recompiling the boot code, and the E (Extensible) means functions can be added and enhanced.

A Lower-Level Operating System
Residing between the computer's startup firmware and the OS, UEFI is able to perform diagnostics, authentication and encryption as well as detect malware. "UEFI BIOS" is often displayed at startup because people are familiar with the meaning of BIOS and still refer to UEFI as the BIOS. See BIOS.

BIOS and UEFI Components
The BIOS master boot record (MBR) and the UEFI GUID partition table (GPT) store the size of the partitions on the storage drive. Whereas MBR supports partitions up to 2.2TB, GPT partitions can be as large as 18 exabytes. See MBR and GPT.