Basic Input/output System (BIOS) served as the OS-firmware interface for the
original PC-XT and PC-AT computers. This interface has been expanded over the
years as the "PC clone" market has grown, but was never fully
modernized as the market grew. UEFI defines a similar OS-firmware interface,
known as "boot services" and "runtime services", but is not
specific to any processor architecture. BIOS is specific to the Intel x86
processor architecture, as it relies on the 16-bit "real mode"
interface supported by x86 processors.