UEFIfirmware

UEFIfirmware refers to the firmware that implements the Unified Extensible Firmware Interface specification. It replaces the traditional BIOS in most modern PCs and servers, performing hardware initialization during boot and preparing the system to load an operating system. UEFIfirmware runs in a pre-boot environment and provides services to the OS and its bootloader.

It is organized into phases such as Pre-EFI Initialization (PEI) and Driver Execution Environment (DXE), followed by Boot Device Selection (BDS) and then transitions to the operating system. PEI initializes essential hardware, DXE loads and configures drivers, BDS selects the boot device, and the DXE phase may continue to supply runtime services after boot.

The UEFI specification defines a standard interface, including the EFI System Table, boot services, and runtime services, which enable the OS and bootloaders to interact with firmware in a consistent manner. The firmware can host drivers and applications, and supports features such as a firmware-based boot manager and user interface. The architecture supports modular upgrades and vendor-specific extensions while maintaining interoperability with compliant operating systems.

Security features include Secure Boot, which validates bootloaders and kernels with cryptographic signatures, and measured boot or attestation in conjunction with a trusted platform module. These features help protect against tampering during pre-boot. UEFIfirmware may also provide compatibility options for legacy BIOS boot in some devices.

Open-source and vendor implementations include the TianoCore EDK II reference implementation and coreboot, which can load UEFI payloads. Commercial firmware from major vendors incorporates UEFIfirmware with device-specific drivers and management interfaces. It is standard in most modern personal computers, servers, and many embedded systems, enabling flexible boot options and modern boot security.