Explanation

BIOS, in full Basic Input/output System, Computer program that is typically stored in EPROM and used by the CPU to perform start-up procedures when the computer is turned on.
In computing, BIOS is firmware used to perform hardware initialization during the booting process, and to provide runtime services for operating systems and programs. The BIOS firmware comes pre-installed on a personal computer's system board, and it is the first software to run when powered on.