Editing BIOS (section)

== Configuration ==
=== Setup utility ===
Historically, the BIOS in the IBM PC and XT had no built-in user interface. The BIOS versions in earlier PCs (XT-class) were not software configurable; instead, users set the options via [[DIP switch]]es on the motherboard. Later computers, including most IBM-compatibles with 80286 CPUs, had a battery-backed [[nonvolatile BIOS memory]] (CMOS RAM chip) that held BIOS settings.<ref name="CMOS Battery"/> These settings, such as video-adapter type, memory size, and hard-disk parameters, could only be configured by running a configuration program from a disk, not built into the ROM. A special "reference diskette" was inserted in an [[IBM Personal Computer/AT|IBM AT]] to configure settings such as memory size.<ref>{{cite book | url=https://books.google.com/books?id=56TT-cJeP9wC&dq=bios+cmos&pg=PA358 | title=PC Systems, Installation and Maintenance | isbn=978-1-136-37441-8 | last1=Beales | first1=R. P. | date=11 August 2006 | publisher=Routledge }}</ref>

Early BIOS versions did not have passwords or boot-device selection options. The BIOS was hard-coded to boot from the first floppy drive, or, if that failed, the first hard disk. Access control in early AT-class machines was by a physical keylock switch (which was not hard to defeat if the computer case could be opened). Anyone who could switch on the computer could boot it.{{citation needed|date=March 2013}}

Later, 386-class computers started integrating the BIOS setup utility in the ROM itself, alongside the BIOS code; these computers usually boot into the BIOS setup utility if a certain key or key combination is pressed, otherwise the BIOS POST and boot process are executed.

[[File:Award BIOS setup utility.png|thumb|Award BIOS setup utility on a standard PC]]
A modern BIOS setup utility has a [[text user interface]] (TUI) or [[graphical user interface]] (GUI) accessed by pressing a certain key on the keyboard when the PC starts. Usually, the key is advertised for short time during the early startup, for example "Press DEL to enter Setup". 

The actual key depends on specific hardware. The settings key is most often [[Delete key|Delete]] ([[Acer Inc.|Acer]], [[ASRock]], [[Asus]] PC, [[Elitegroup Computer Systems|ECS]], [[Gigabyte Technology|Gigabyte]], [[Micro-Star International|MSI]], [[ZOTAC|Zotac]]) and [[Function key|F2]] (Asus&nbsp;motherboard, [[Dell]], [[Lenovo]] laptop, [[Origin PC]], [[Samsung]], [[Toshiba]]), but it can also be [[Function key|F1]] (Lenovo&nbsp;desktop) and [[Function key|F10]] ([[Hewlett-Packard|HP]]).<ref>{{cite news |title=How to Enter the BIOS on Any PC: Access Keys by Manufacturer |url=https://www.tomshardware.com/reviews/bios-keys-to-access-your-firmware,5732.html |work=Tom's Hardware |date=4 February 2022 |language=en}}</ref>

Features present in the BIOS setup utility typically include:

* Configuring, enabling and disabling the hardware components
* Setting the [[system time]]
* Setting the boot order
* Setting various passwords, such as a password for securing access to the BIOS user interface and preventing malicious users from booting the system from unauthorized portable storage devices, or a password for booting the system

=== Hardware monitoring ===
{{Main|Hardware monitoring}}
A modern BIOS setup screen often features a '''PC Health Status''' or a '''Hardware Monitoring''' tab, which directly interfaces with a Hardware Monitor chip of the mainboard.<ref name=sensors-mmath>{{cite thesis
|degree= [[Master of Mathematics#Canada|MMath]]
|author= Constantine A. Murenin |date= 2010-05-21
|section = 11.1. Interfacing from the BIOS
|title= OpenBSD Hardware Sensors – Environmental Monitoring and Fan Control.
|location= [[University of Waterloo]] |publisher= UWSpace
|url = http://cnst.su/MMathCS |hdl = 10012/5234
|id = Document ID: ab71498b6b1a60ff817b29d56997a418.
}}</ref> This makes it possible to monitor CPU and [[computer case|chassis]] temperature, the voltage provided by the [[power supply unit (computer)|power supply unit]], as well as monitor and [[computer fan control|control the speed of the fans]] connected to the motherboard.

Once the system is booted, hardware monitoring and [[computer fan control]] is normally done directly by the Hardware Monitor chip itself, which can be a separate chip, interfaced through [[I²C]] or [[System Management Bus|SMBus]], or come as a part of a [[Super I/O]] solution, interfaced through [[Industry Standard Architecture]] (ISA) or [[Low Pin Count]] (LPC).<ref name=ieee07>{{Cite conference
|author= Constantine A. Murenin |date= 2007-04-17
|url = http://sensors.cnst.su/IEEE_ICNSC_2007
|section = 2. Hardware review
|title= Generalised Interfacing with Microprocessor System Hardware Monitors
|conference= Proceedings of 2007 IEEE International Conference on Networking, Sensing and Control, 15–17 April 2007.
|location= London, United Kingdom
|publisher=[[Institute of Electrical and Electronics Engineers|IEEE]]
|pages = 901–906 |doi = 10.1109/ICNSC.2007.372901 |isbn = 978-1-4244-1076-7
|id = IEEE ICNSC 2007, pp. 901—906.
}}</ref> Some operating systems, like [[NetBSD]] with [[envsys]] and [[OpenBSD]] with sysctl [[hw.sensors]], feature integrated interfacing with hardware monitors.

However, in some circumstances, the BIOS also provides the underlying information about hardware monitoring through [[Advanced Configuration and Power Interface|ACPI]], in which case, the operating system may be using ACPI to perform hardware monitoring.<ref name=aibs.4>{{cite web|url=http://mdoc.su/-/aibs.4|title=aibs – ASUSTeK AI Booster ACPI ATK0110 voltage, temperature and fan sensor|publisher=[[OpenBSD]], [[DragonFly BSD]], [[NetBSD]] and [[FreeBSD]]|date=2010}}</ref><ref>{{Cite web|title=acpi_thermal(4)|url=https://www.freebsd.org/cgi/man.cgi?query=acpi_thermal&sektion=4|access-date=2021-02-24|website=www.freebsd.org}}</ref>

=== {{anchor|Flashing the BIOS}}Reprogramming ===
[[File:BIOS replacement kit.jpg|right|thumb|BIOS replacement kit for a Dell 310 from the late 1980s. Included are two chips, a plastic holder for the chips, and a [[IC extractor]].]]
In modern PCs the BIOS is stored in rewritable [[EEPROM]]<ref>{{cite book | url=https://books.google.com/books?id=V48MZCwICH8C&dq=bios+eeprom&pg=PA180 | title=CompTIA A+ Certification All-In-One Desk Reference for Dummies | isbn=978-0-471-74811-3 | last1=Clarke | first1=Glen E. | last2=Tetz | first2=Edward | date=30 January 2007 | publisher=John Wiley & Sons }}</ref> or [[NOR flash memory]],<ref>{{cite book | url=https://books.google.com/books?id=vaq11vKwo_kC&dq=bios+nor+flash&pg=PA2 | title=Inside NAND Flash Memories | isbn=978-90-481-9431-5 | last1=Micheloni | first1=Rino | last2=Crippa | first2=Luca | last3=Marelli | first3=Alessia | date=27 July 2010 | publisher=Springer }}</ref> allowing the contents to be replaced and modified. This rewriting of the contents is sometimes termed ''flashing.'' It can be done by a special program, usually provided by the system's manufacturer, or at [[power-on self-test|POST]], with a BIOS image in a hard drive or USB flash drive. A file containing such contents is sometimes termed "a BIOS image". A BIOS might be reflashed in order to upgrade to a newer version to fix bugs or provide improved performance or to support newer hardware. Some computers also support updating the BIOS via an update floppy disk or a special partition on the hard drive.<ref>{{cite book | url=https://books.google.com/books?id=E1p2FDL7P5QC&dq=bios+cmos&pg=PA393 | title=Upgrading and Repairing PCS | isbn=978-0-7897-2974-3 | last1=Mueller | first1=Scott | date=2004 | publisher=Que }}</ref>