computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...
, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of
firmware
In computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...
used to provide runtime services for
operating system
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
s and programs and to perform hardware initialization during the
booting
In computing, booting is the process of starting a computer as initiated via Computer hardware, hardware such as a physical button on the computer or by a software command. After it is switched on, a computer's central processing unit (CPU) h ...
process (power-on startup). The firmware comes pre-installed on the computer's
motherboard
A motherboard, also called a mainboard, a system board, a logic board, and informally a mobo (see #Nomenclature, "Nomenclature" section), is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It ho ...
.
The name originates from the Basic Input/Output System used in the
CP/M
CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/Intel 8085, 85-based microcomputers by Gary Kildall of Digital Research, Dig ...
operating system in 1975. The BIOS firmware was originally
proprietary
{{Short pages monitor
The operating system OpenBSD prevents all users from having this access and the grsecurity patch for the Linux kernel also prevents this direct hardware access by default, the difference being an attacker requiring a much more difficult kernel level exploit or reboot of the machine.
The third BIOS virus was a technique presented by John Heasman, principal security consultant for UK-based Next-Generation Security Software. In 2006, at the Black Hat Security Conference, he showed how to elevate privileges and read physical memory, using malicious procedures that replaced normal Advanced Configuration and Power Interface, ACPI functions stored in flash memory.
The fourth BIOS virus was a technique called "Persistent BIOS infection." It appeared in 2009 at the CanSecWest Security Conference in Vancouver, and at the SyScan Security Conference in Singapore. Researchers Anibal Sacco and Alfredo Ortega, from Core Security Technologies, demonstrated how to insert malicious code into the decompression routines in the BIOS, allowing for nearly full control of the PC at start-up, even before the operating system is booted. The proof-of-concept does not exploit a flaw in the BIOS implementation, but only involves the normal BIOS flashing procedures. Thus, it requires physical access to the machine, or for the user to be root. Despite these requirements, Ortega underlined the profound implications of his and Sacco's discovery: "We can patch a driver to drop a fully working
rootkit
A rootkit is a collection of computer software, typically malicious, designed to enable access to a computer or an area of its software that is not otherwise allowed (for example, to an unauthorized user) and often masks its existence or the exist ...
. We even have a little code that can remove or disable antivirus."
Mebromi is a Trojan horse (computing), trojan which targets computers with AwardBIOS,
Microsoft Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
, and antivirus software from two Chinese companies: Rising Antivirus and Jiangmin KV Antivirus. Mebromi installs a rootkit which infects the Master boot record.
In a December 2013 interview with ''60 Minutes'', Deborah Plunkett, Information Assurance Director for the US National Security Agency claimed the NSA had uncovered and thwarted a possible BIOS attack by a foreign nation state, targeting the US financial system. The program cited anonymous sources alleging it was a Chinese plot. However follow-up articles in ''The Guardian,'' ''The Atlantic,'' ''Wired (magazine), Wired'' and ''The Register'' refuted the NSA's claims.
Newer Intel platforms have Intel Boot Guard (IBG) technology enabled, this technology will check the BIOS digital signature at startup, and the IBG public key is fused into the Platform Controller Hub, PCH. End users can't disable this function.
Alternatives and successors
UEFI, Unified Extensible Firmware Interface (UEFI) supplements the BIOS in many new machines. Initially written for the Intel Itanium architecture, UEFI is now available for x86 and ARM architecture family, Arm platforms; the specification development is driven by the Unified EFI Forum, an industry special interest group. EFI booting has been supported in only
Microsoft Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
versions supporting GUID Partition Table, GPT, the Linux kernel 2.6.1 and later, and macOS on Apple–Intel architecture, Intel-based Macs. , new PC hardware predominantly ships with UEFI firmware. The architecture of the rootkit safeguard can also prevent the system from running the user's own software changes, which makes UEFI controversial as a legacy BIOS replacement in the open hardware community. Also,
Windows 11
Windows 11 is a version of Microsoft's Windows NT operating system, released on October 5, 2021, as the successor to Windows 10 (2015). It is available as a free upgrade for devices running Windows 10 that meet the #System requirements, Windo ...
requires UEFI to boot, with the exception of IoT Enterprise editions of Windows 11. UEFI is required for devices shipping with Windows 8 and above.
After the popularity of UEFI in 2010s, the older BIOS that supported
BIOS interrupt call
BIOS implementations provide interrupts that can be invoked by operating systems and application programs to use the facilities of the firmware on IBM PC compatible computers. Traditionally, BIOS calls are mainly used by DOS programs and some ot ...
s was renamed to "legacy BIOS".
Other alternatives to the functionality of the "Legacy BIOS" in the x86 world include coreboot and libreboot.
Some servers and workstations use a platform-independent Open Firmware (IEEE-1275) based on the Forth (programming language), Forth programming language; it is included with Sun's SPARC computers, IBM's RS/6000 line, and other PowerPC systems such as the Common Hardware Reference Platform, CHRP motherboards, along with the x86-based OLPC XO-1.
As of at least 2015, Apple Inc., Apple has removed legacy BIOS support from the UEFI monitor in Apple-Intel architecture, Intel-based Macs. As such, the BIOS utility no longer supports the legacy option, and prints "Legacy mode not supported on this system".
In 2017, Intel announced that it would remove legacy BIOS support by 2020. Since 2019, new Intel platform OEM PCs no longer support the legacy option.
See also
* Double boot
* Extended System Configuration Data (ESCD)
* Input/Output Control System
* ACPI (Advanced Configuration and Power Interface)
* Ralf Brown's Interrupt List (RBIL)interrupts, calls, interfaces, data structures, memory and port addresses, and processor opcodes for the x86 architecture
* System Management BIOS (SMBIOS)
* UEFI (Unified Extensible Firmware Interface)
* Das U-Boot, often used on embedded systems