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Bios or BIOS may refer to:

• Life (in Greek, βίος/Bios)
• Biographies, a genre of literature/media based on accounts of people's lives
• BIOS, the Basic Input/Output System of a computer
• Biological Innovation for Open Society
• The British Institute of Organ Studies
• BIOS (journal), a quarterly journal of biology
• BIOS Group, a Santa Fe, New Mexico-based for-profit company that employs complex systems methodology to attempt to solve business problems
• Bios (band), a power noise group
• BIOS Faction in the Allegiance (computer game)
• BIOS is the society journal of the Tri Beta society
• BIOS British Intelligence Objectives Sub-comittee
• BIOS Centre for the Study of Bioscience, Biomedicine, Biotechnology and Society at the London School of Economics and Political Science, United Kingdom

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BIOS: Basic Input/Output System

Phoenix AwardBIOS CMOS (non-volatile memory) Setup utility on a standard PC

Stored on: PROM EPROM Flash memory

Common Manufacturers: American Megatrends Phoenix Technologies Others

BIOS (pronounced [ˈbaɪoʊs]), in computing, stands for Basic Input/Output System.^{[1] [2]}

The term is incorrectly known as Binary Input/Output System, Basic Integrated Operating System and occasionally Built In Operating System. BIOS refers to the firmware code run by a personal computer when first powered on. The primary function of the BIOS is to identify and initiate component hardware, (such as hard drives, floppies, and CDs). This is to prepare the machine so other software programs stored on various media can load, execute, and assume control of the PC^[3]. This process is known as booting, or booting up, which is short for bootstrapping.

BIOS can also be said to be a coded program embedded on a chip that recognizes and controls various devices that make up x86 personal computers. Among other classes of computers, the generic terms boot monitor, boot loader or boot ROM were commonly used. Some Sun and Macintosh PowerPC computers used Open Firmware for this purpose. There are a few proposed alternatives for Legacy BIOS on the x86 world: Extensible Firmware Interface, Open Firmware (used on the OLPC) and LinuxBIOS.

The term first appeared in the CP/M operating system, describing the part of CP/M loaded during boot time that interfaced directly with the hardware (CP/M machines usually had a simple boot loader in ROM, and nothing else). Most versions of DOS have a file called "IBMBIO.COM" or "IO.SYS" that is analogous to the CP/M disk BIOS.

How the BIOS boots

#	Layer
0	Hardware
1	System BIOS
2	Operating system
3	Application

The BIOS runs from the PROM, EPROM or, most commonly, flash memory when the computer is powered on. It initializes several motherboard components and peripherals, including:

• the clock generator,
• the processors and caches,
• the chipset (memory controller and I/O controller),
• the system memory,
• all PCI devices (by assigning bus numbers and resources),
• the primary graphics controller,
• mass storage controllers (such as SATA and IDE controllers),
• various I/O controllers (such keyboard/mouse and USB).

Finally, it loads the boot loader for the operating system, and transfers control to it. The entire process is known as Power-on self-test (POST). On the original IBM PC, the hardware only needed minimal configuration and POST was indeed used for testing; on modern systems, most of POST actually consists of hardware configuration.

Once system memory is initialized, the BIOS typically copies/decompresses itself into that memory and keeps executing from it.

Nearly all BIOS implementations can optionally execute a setup program interfacing the nonvolatile BIOS memory (CMOS). This memory holds user-customizable configuration data (passwords, time, date, hard drive details, etc.) accessed by BIOS code. The 80x86 source code for early PC and AT BIOS was included with the IBM Technical Reference Manual.

In most modern BIOS implementations, users select which device boots first: CD, hard disk, floppy disk, USB device, and the like. This is particularly useful for installing operating systems or booting to a Live CD or flash keydrive, and for selecting the order of testing for the presence of bootable media.

Some BIOS's allow the user to select the operating system to load (e.g. load another OS from the second hard disk), though this is more often handled by a second-stage boot loader.

The BIOS Chip and BIOS Recovery

Before 1990 or so BIOSes were held on ROM chips that could not be altered. As its complexity and need for updates grew, BIOS firmware was subsequently stored on EEPROM or flash memory devices. The first flash chips attached to the ISA bus. Starting in 1998, the BIOS flash moved to the LPC bus, a functional replacement for ISA, following a new standard implementation known as "firmware hub" (FWH). In 2006, the first systems supporting a Serial Peripheral Interface (SPI) appeared, and the BIOS flash moved again.

EEPROM chips are advantageous because they can easily be updated by the user; hardware manufacturers frequently issue BIOS updates to upgrade their products, improve compatibility and remove bugs. However, the risk is that an improperly executed or aborted BIOS update can render the computer or device unusable. To recover from BIOS corruption, some new motherboards have a backup BIOS (i.e. they are referred to as "Dual BIOS" boards, Gigabyte even offers a motherboard with quad BIOS). Also, most BIOSes have a "boot block" which is a portion of the ROM that runs first and is not updateable. This code will verify that the rest of the BIOS is intact (via checksum, hash, etc.) before transferring control to it. If the boot block detects that the main BIOS is corrupted, then it will typically initiate a recovery process, by booting to a removable device (floppy, CD or USB memory) so that the user can try flashing again.

Due to the limitation on the number of times that flash memory can be flashed, a flash-based BIOS is vulnerable to "flash-burn" viruses that repeatedly write to the flash, permanently corrupting the chip. Such attacks can be prevented by some form of write-protection, the ultimate protection being the replacement of the flash memory with a true ROM.

Firmware on adapter cards

A computer system can contain several BIOS firmware chips. The motherboard BIOS typically contains code to access fundamental hardware components such as the keyboard, floppy drives, ATA (IDE) hard disk controllers, USB human interface devices, and storage devices. In addition, plug-in adapter cards such as SCSI, RAID, Network interface cards, and video boards often include their own BIOS, complementing or replacing the system BIOS code for the given component.

In some devices that can be used by add-in adapters and actually directly integrated on the motherboard, the add-in ROM may also be stored as separate code on the main BIOS flash chip. It may then be possible to upgrade this "add-in" BIOS (sometimes called an option ROM) separately from the main BIOS code.

Add-in cards usually only require such an add-in BIOS if they:

• Need to be used prior to the time that the operating system loads (e.g. they may be used as part of the process which loads (bootstraps) the operating system), and:
• Are not sufficiently simple, or generic in operation to be handled by the main BIOS directly

Older operating systems such as DOS, as well as bootloaders, may continue to make use of the BIOS to handle input and output. However, most modern operating systems will interact with hardware devices directly by using their own device drivers to directly access the hardware. Occasionally these add-in BIOSs are still called by modern operating systems, in order to carry out specific tasks such as preliminary device initialization.

To find these memory mapped expansion ROMs during boot, PC BIOS implementations scan real memory from 0xC8000 to 0xF0000 on 2 kibibyte boundaries looking for a 0x55 0xaa signature, which is immediately followed by a byte indicating the number of 512 byte blocks the expansion ROM occupies in real memory. The BIOS then jumps to the offset immediately after the size byte, at which point the expansion ROM code takes over and uses BIOS services to provide a user configuration interface, register interrupt vectors for use by post-boot applications, or display diagnostic information.

For UNIX and Windows/DOS systems there is a utility with which BIOS firmware software can be dumped at [1]
There is a tool to flash the BIOS from Linux at [2]

The BIOS boot specification

If the expansion ROM wishes to change the way the system boots (such as from a network device or a SCSI adapter for which the BIOS has no driver code), it can use the BIOS Boot Specification (BBS) API to register its ability to do so. Once the expansion ROMs have registered using the BBS APIs, the user can select among the available boot options from within the BIOS's user interface. This is why most BBS compliant PC BIOS implementations will not allow the user to enter the BIOS's user interface until the expansion ROMs have finished executing and registering themselves with the BBS API.

Evolution of the role of the BIOS

Older Personal Computer operating systems, which were developed for 16-bit CPUs, such as MS-DOS, relied on the BIOS to carry out most input-output tasks within the PC. A variety of technical reasons eventually made it inefficient for more recent operating systems written for 32-bit CPUs such as Linux and Microsoft Windows to invoke the BIOS directly. Larger, more powerful, servers and workstations using PowerPC or SPARC CPUs by several manufacturers developed a platform-independent Open Firmware(IEEE-1275), based on the Forth programming language. It is included with Sun's Sparc computers, IBM's RS/6000 line, and other PowerPC CHRP motherboards. Later x86-based personal computer operating systems, like Windows NT, use their own, better-performing, native drivers and also made it much easier to extend support to new hardware, while BIOS still relies on a legacy 16-bit runtime interface. As such, the BIOS was relegated to bootstrapping, at which point the operating system's own drivers could take control of the hardware.

There were a similar transitions for the Apple Macintosh, where the system software originally relied heavily on the ToolBox—a set of drivers and other useful routines stored in ROM based on Motorola's 680x0 CPUs. These Apple ROMs were replaced by Open Firmware in the PowerPC Macintosh, then EFI in Intel Macintosh computers.

BIOS had taken on more complex functions, by way of interfaces such as ACPI; these functions include power management, hot swapping and thermal management. However BIOS limitations (16-bit processor mode, only 1 MB addressable space, PC AT hardware dependencies, etc.) were seen as clearly unacceptable for the newer computer platforms. Extensible Firmware Interface (EFI) is a specification which replaces the runtime interface of the legacy BIOS. Initially written for the Itanium architecture, EFI is now available for x86 and x64 platforms; the specification development is driven by The Unified EFI Forum, an industry Special Interest Group.

Linux has supported EFI via elilo boot loader. The Open Source community increased their effort to develop a replacement for proprietary BIOSes and their future incarnations with an open sourced counterpart through the LinuxBIOS and OpenBIOS/Open Firmware projects. AMD provided product specifications for some chipsets, and Google is sponsoring the project. Motherboard manufacturer Tyan offers LinuxBIOS next to the standard BIOS with their Opteron line of motherboards. MSI and Gigabyte have followed suit with the MSI K9ND MS-9282 and MSI K9SD MS-9185 resp. the M57SLI-S4 modems.

The BIOS business

The vast majority of PC motherboard suppliers license a BIOS "core" and toolkit from a commercial third party, known as an "independent BIOS vendor" or IBV. The motherboard manufacturer then customizes this BIOS to suit its own hardware. For this reason, updated BIOSes are normally obtained directly from the motherboard manufacturer.

Major BIOS vendors include American Megatrends (AMI), Insyde Software, and Phoenix Technologies (which bought Award Software International in 1998).

See also

• Firmware
• Extensible Firmware Interface (EFI)
• LinuxBIOS, a project which aim is to create a free replacement for the BIOS
• Open Firmware
• Input/Output Base Address
• Advanced Configuration and Power Interface (ACPI)
• BIOS boot devices
• BIOS Interrupt Calls
• Power-On Self Test (POST)
• Nonvolatile BIOS memory
• ARCS

Sources

• How BIOS Works - HowStuffWorks

External links

• Wim's BIOS Page
• TweakBIOS - BIOS information and tweaking
• BIOS options explained
• Award BIOS identification page
• Information about the BIOS, POST, BIOS recovery
• BIOS from A to Z
• BIOS for Beginners

Notes and References