The unified extensible firmware interface (UEFI) is the specification for software programs that connect a computer's firmware to its operating system (OS) and is expected to eventually replace the BIOS.
Like the BIOS, UEFI is installed at manufacturing time and is the first program to run when the computer is turned on. It checks to see what hardware components the computing device has, wakes them up, and hands them over to the operating system. The new specification addresses some BIOS limitations, including limits on the size of the hard disk partitions and the time it takes the BIOS to perform tasks.
Because UEFI is programmable, original equipment manufacturer (OEM) developers can add applications and drivers to make it work as a lightweight operating system.
The unified extensible firmware interface is managed by a set of chipsets, hardware, systems, firmware, and operating system vendors called UEFI forums. The specification is usually declared by naming the letter UEFI.