In computing, the BIOS (pronounced /ˈbaɪoʊs/) is an acronym that stands either for the Basic Input/Output System or for Built In Operating System (see Acronym definition). The latter term dates from the late 1970s and early 1980s when the PCs of the day normally contained a comprehensive operating system in their ROMs. The latter acronym is still much used in conjunction with gadgetry containing dedicated computers, such as modern cameras, white-wear, etc. The underlying technology is very similar, being little more than a matter of size. BIOS refers, in part, to the firmware code (a type of boot loader) run by a PC when first powered on. The primary function of the BIOS is to identify and initialize system component hardware (such as the video display card, hard disk, and floppy disk) and some other hardware devices. This is to prepare the machine into a known low capability state, so other software programs stored on various media can be loaded, executed, and given control of the PC.[1] This process is known as booting, or booting up, which is short for bootstrapping.
The BIOSes of IBM PC class machines are coded programs embedded on a chip that recognize and control various devices that make up x86 personal computers, and provide a small library of basic Input/Output functions that can be called to operate and control the peripherals such as the keyboard, primitive (800 x 600) display functions and so forth.
Computers designed to run Windows ME or Windows 2000, or later, supersede this basic monitor functionality by taking over direct control of the interrupt table and replacing the monitor routines with faster and more robust low-level modules that, unlike the BIOS function set, are re-entrant. Various BIOS functions in ROM were left in control in earlier Windows versions, and the BIOS only comes into play today in the alternate shell Cmd.exe, or if the machine is booted into a legacy DOS version
