Description
In IBM
PC compatible computers, the Basic Input/Output System (BIOS), also known as System BIOS, ROM BIOS or PC BIOS (/ˈbaɪ.oʊs/), is a de
facto standard defining a firmware interface. The name originated from the Basic
Input/Output System used in the CP/M operating system in 1975. The BIOS software is built into the PC,
and is the first software run by a PC when powered on.
The fundamental purposes of the
BIOS are to initialize and test the system hardware components, and to load a bootloader or an operating
system from a mass memory
device. The BIOS additionally provides abstraction layer for the hardware, i.e.
a consistent way for application programs and operating systems to interact
with the keyboard, display, and other input/output devices. Variations in the
system hardware are hidden by the BIOS from programs that use BIOS services
instead of directly accessing the hardware. Modern operating systems ignore the
abstraction layer provided by the BIOS and access the hardware components directly.
The BIOS of the original IBM
PC/XT had no interactive user interface. Error messages were displayed on the
screen, or coded series of sounds were generated to signal errors. Options on
the PC and XT were set by switches and jumpers on the main board and on
peripheral cards. Modern Wintel-compatible
computers provide a setup routine, accessed at system power-up by a particular
key sequence. The user can configure hardware options using the keyboard and
video display.
BIOS software is stored on a non-volatile ROM chip on the motherboard.
It is specifically designed to work with each particular model of computer,
interfacing with various devices that make up the complementary chipset of the
system. In modern computer systems, the BIOS contents are stored on a flash
memory chip so that the
contents can be rewritten without removing the chip from the motherboard. This
allows BIOS software to be easily upgraded to add new features or fix bugs, but
can make the computer vulnerable to BIOS rootkits.
MS-DOS (PC DOS), which
was the dominant PC operating system from the early 1980s until the mid 1990s,
relied on BIOS services for disk, keyboard, and text display functions. MS
Windows NT, Linux, and other protected
mode operating systems in
general do not use it after loading.
BIOS technology is in
transitional process toward the Unified Extensible Firmware
Interface (UEFI) since 2010.
The term BIOS (Basic Input/Output
System) was invented by Gary
Kildall and first appeared in
the CP/M operating system in 1975, describing the machine-specific part
of CP/M loaded during boot time that interfaces directly with the hardware. (A CP/M machine usually has only a
simple boot loader in its ROM.)
With the introduction of
PS/2 machines, IBM divided the System BIOS into real-mode and protected mode
portions. The real-mode portion was meant to provide backward-compatibility
with existing operating systems such as DOS, and therefore was named
"CBIOS" (for Compatibility BIOS), whereas the "ABIOS" (for
Advanced BIOS) provided new interfaces specifically suited for multitasking
operating systems such as OS/2
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