Editing BIOS (section)

{{Short description|Firmware for hardware initialization and OS runtime services}}
{{About|the BIOS as found in IBM PC/AT and compatibles|the modern replacement that is often still called BIOS|UEFI|the general concept|Firmware||Bios (disambiguation)}}
{{Use dmy dates|date=October 2020|cs1-dates=y}}
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| caption           = A pair of [[Advanced Micro Devices|AMD]] BIOS chips for a [[Dell]] 310 computer from the 1980s. The bottom one shows the distinct window of an [[EPROM]] chip.
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| year_started      = 1981{{efn|Although the term BIOS predates 1981, the standard for [[IBM PC–compatible]] computers started with the release of the original [[IBM Personal Computer]].}}
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| organization      = Originally [[IBM]] as proprietary software, later industry wide as a [[de facto]] standard. In 1996, the ''BIOS Boot Specification'' was written by [[Compaq]], [[Phoenix Technologies]] and [[Intel]]. 
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| successor         = [[UEFI]]
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In [[computing]], '''BIOS''' ({{IPAc-en|ˈ|b|aɪ|ɒ|s|,_|-|oʊ|s}}, {{respell|BY|oss|,_|-|ohss}}; '''Basic Input/Output System''', also known as the '''System BIOS''', '''ROM BIOS''', '''BIOS ROM''' or '''PC BIOS''') is a type of [[firmware]] used to provide runtime services for [[operating system]]s and [[Computer program|programs]] and to perform [[Computer hardware|hardware]] initialization during the [[booting]] process (power-on startup).<ref name="pcguidedefinition" /> The firmware comes pre-installed on the computer's [[motherboard]].

The name originates from the '''B'''asic '''I'''nput/'''O'''utput '''S'''ystem used in the [[CP/M]] operating system in 1975.<ref name="Kildall_1975_BDOS" /><ref name="Kildall_1980_CPM" /> The BIOS firmware was originally [[Proprietary software|proprietary]] to the [[IBM PC]]; it was [[reverse engineer]]ed by some companies (such as [[Phoenix Technologies]]) looking to create compatible systems. The [[Interface (computing)|interface]] of that original system serves as a [[De facto standard|''de facto'' standard]].

The BIOS in older PCs initializes and tests the system hardware components ([[power-on self-test]] or POST for short), and loads a [[boot loader]] from a mass storage device which then initializes a [[kernel (operating system)|kernel]]. In the era of [[DOS]], the BIOS provided [[BIOS interrupt call]]s for the keyboard, display, storage, and other [[input/output]] (I/O) devices that standardized an interface to application programs and the operating system. More recent operating systems do not use the BIOS interrupt calls after startup.<ref name="Booting · Linux Inside">{{Cite web|title=Booting · Linux Inside|url=https://0xax.gitbooks.io/linux-insides/content/Booting/|access-date=2020-11-10|website=0xax.gitbooks.io}}</ref>

Most BIOS implementations are specifically designed to work with a particular computer or [[motherboard]] model, by interfacing with various devices especially system [[chipset]]. Originally, BIOS firmware was stored in a [[Read-only memory|ROM]] chip on the PC motherboard. In later computer systems, the BIOS contents are stored on [[flash memory]] so it can be rewritten without removing the chip from the motherboard. This allows easy, end-user updates to the BIOS firmware so new features can be added or bugs can be fixed, but it also creates a possibility for the computer to become infected with BIOS [[rootkit]]s. Furthermore, a BIOS upgrade that fails could [[brick (electronics)|brick]] the motherboard.

[[Unified Extensible Firmware Interface]] (UEFI) is a successor to the PC BIOS, aiming to address its technical limitations.<ref name="Bradley" /> UEFI firmware may include legacy BIOS compatibility to maintain compatibility with operating systems and option cards that do not support UEFI native operation.<ref>{{cite web |title=Unified Extensible Firmware Interface|url=https://www.intel.com/content/www/us/en/developer/articles/tool/unified-extensible-firmware-interface.html |website=Intel }}</ref><ref>{{cite web |title=UEFI |url=https://wiki.osdev.org/UEFI |website=OSDev.org |ref=Legacy_bootloader_or_UEFI_application.3F}}</ref><ref>{{cite web |url=http://www.intel.com/content/dam/doc/reference-guide/efi-compatibility-support-module-specification-v097.pdf |title=Intel® Platform Innovation Framework for EFI Compatibility Support Module Specification (revision 0.97) |date=4 September 2007 |access-date=6 October 2013 |publisher=Intel}}</ref> Since 2020, all PCs for Intel platforms no longer support legacy BIOS.<ref>{{Cite web |title=Removal of Legacy Boot Support for Intel Platforms Technical Advisory |url=https://www.intel.com/content/www/us/en/content-details/630266/removal-of-legacy-boot-support-for-intel-platforms-technical-advisory.html |access-date=2024-07-25}}</ref> The last version of [[Microsoft Windows]] to officially support running on PCs which use legacy BIOS firmware is [[Windows 10]] as [[Windows 11]] requires a UEFI-compliant system (except for IoT Enterprise editions of Windows 11 since [[Windows 11, version 24H2|version 24H2]]<ref name=11_IoT_req>{{Cite web|date=May 22, 2024 |title=Minimum System Requirements for Windows IoT Enterprise|url=https://learn.microsoft.com/en-gb/windows/iot/iot-enterprise/Hardware/System_Requirements?tabs=Windows11|access-date=June 7, 2024 |website=[[Microsoft Learn]]}}</ref>).