UEFI

UEFI, short for Unified Extensible Firmware Interface, is a specification that defines a software interface between an operating system and platform firmware. Developed to replace the traditional BIOS, UEFI provides a more flexible, modular, and scalable environment for booting and initializing hardware. It is a standard that firmware implementations can adhere to, rather than a single piece of code.

Key concepts in UEFI include boot services, which run during pre-boot initialization, and runtime services, which persist after the operating system starts. UEFI firmware environments are typically 32- or 64-bit and commonly work with the GUID Partition Table (GPT), enabling booting from disks larger than 2 terabytes and supporting richer partition metadata. The EFI System Partition stores bootloaders, drivers, and utilities.

Security features include Secure Boot, a mechanism that validates the digital signatures of bootloaders, kernels, and other early-stage software to ensure only trusted software executes during startup. Secure Boot uses platform keys and signing keys and can be configured or disabled to accommodate alternative operating systems or development workflows.

Compatibility with older operating systems is provided by the Compatibility Support Module (CSM), which emulates BIOS-like booting for legacy software. While many systems boot in UEFI mode, some firmware implementations offer mixed modes that support both UEFI and legacy BIOS boot paths. UEFI also supports network boot and modular loading of drivers and option ROMs.

UEFI originated with Intel in the 1990s and was standardized and expanded by the UEFI Forum, an industry consortium that includes major hardware and software companies. Today, UEFI is widely adopted on modern PCs and servers and is supported by major operating systems, including Windows and Linux. It represents a shift from BIOS toward a modern, extensible pre-boot environment.