Basic Input/Output System (BIOS)

The Basic Input/Output System commonly known as BIOS is a piece of software that is stored in the computer to allow it control basic hardware and boot an operating system. BIOS provides a standard interface so that software can access the computer hardware without having to know the specific details of each component.

The BIOS is usually stored in a chip located on the system motherboard. There are different types of BIOS chips, orginally most BIOS information was stored in a ROM (Read Only Memory) chip, which meant to upgrade the BIOS you needed to replace the chip. In modern PCs the BIOS is usually stored in a flash memory chip, which means the chip can be flashed (re-written) to upgrade or change the BIOS.

Since reading the BIOS from this chip is usually slower that reading from RAM, most PCs allow the BIOS to be copied to RAM on boot-up and read from there instead which is known as shadowing.