Legacy BIOS mode is the traditional type of booting up a computer introduced long before UEFI in 1984 when IBM released the first Personal Computer. It was more common to boot earlier versions of Windows OS like 95, 98, XP, Vista, 7, and 8, and it is still accessible in recent Windows 10 & 11.
The look of BIOS legacy mode is straightforward, with a blue/gray background and text-only interface.