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For other uses, see Bios. In Computing, the BIOS (ˈbaɪoʊs
BIOS: Basic Input/Output System

Phoenix AwardBIOS CMOS (non-volatile memory) Setup utility on a standard PC
Stored on:
Common Manufacturers:

BIOS (pronounced /ˈbaɪoʊs/), in computing, stands for Basic Input/Output System. Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information A programmable read-only memory ( PROM) or field programmable read-only memory ( FPROM) is a form of digital memory where the setting of each bit is An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed American Megatrends Incorporated ( AMI) is a hardware and Software company headquartered in unincorporated Gwinnett County, Phoenix Technologies Ltd ( is a creator of computer BIOS software In Computing, the BIOS (ˈbaɪoʊs Computing is usually defined like the activity of using and developing Computer technology Computer hardware and software. [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 an IBM PC when first powered on. In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. The primary function of the BIOS is to identify and initiate component hardware (such as hard disk, floppy and optical disk drives). A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device A floppy disk is an increasingly Obsolete data storage medium that is composed of a disk of thin flexible ("floppy" Magnetic storage medium encased In Computing, an optical disc drive ( ODD) is a Disk drive that uses Laser light or electromagnetic waves near the Light spectrum 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. In computing bootstrapping ("to pull oneself up by one's bootstraps" refers to techniques that allow a simple system to activate a more complicated system

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. See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal Among other classes of computers, the generic terms boot monitor, boot loader or boot ROM were commonly used. A boot monitor is a small interactive Computer program that allows a computer operator to load an Operating system. In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system Some Sun and Macintosh PowerPC computers used Open Firmware for this purpose. Open Firmware, or OpenBoot in Sun Microsystems parlance is a standard defining the interfaces of a computer Firmware system formerly endorsed by the There are a few proposed alternatives for Legacy BIOS in the x86 world: Extensible Firmware Interface, Open Firmware (used on the OLPC XO-1) and coreboot. The Extensible Firmware Interface ( EFI) is a specification that defines a software Interface between an Operating system and platform Firmware Open Firmware, or OpenBoot in Sun Microsystems parlance is a standard defining the interfaces of a computer Firmware system formerly endorsed by the The XO-1, previously known as the $100 Laptop or Children's Machine, is an inexpensive Laptop computer intended to be distributed to children in developing Coreboot (formerly known as LinuxBIOS is a Free software project endorsed by the Free Software Foundation, aimed at replacing the standard BIOS Firmware

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). CP/M (Control Program for Microcomputers is an Operating system originally created for Intel 8080 / 85 based Microcomputers by Gary Kildall Typical PC hardware A typical Personal computer consists of a case or chassis in a tower shape (desktop and the following parts Motherboard Most versions of DOS have a file called "IBMBIO.COM" or "IO.SYS" that is analogous to the CP/M disk BIOS. DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market IBMBIOCOM is a filename used by the Boot loader for several DOS operating systems IOSYS is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS Device drivers (hardware interfacing routines and the DOS initialization

Contents

The BIOS Chip and BIOS Recovery

Boot Block
DMI Block
Main Block
ROM with BIOS
ROM with BIOS

Prior to the early 1990s, BIOSes were stored in ROM or PROM chips, which could not be altered by users. A programmable read-only memory ( PROM) or field programmable read-only memory ( FPROM) is a form of digital memory where the setting of each bit is As its complexity and need for updates grew, and re-programmable parts became more available, BIOS firmware was most commonly stored on EEPROM or flash memory devices. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed The first flash chips attached to the ISA bus. Industry Standard Architecture (in practice almost always shortened to ISA) was a Computer bus standard for IBM compatible computers 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). The Low Pin Count bus or LPC bus, is used on IBM-compatible Personal computers to connect low-bandwidth devices to the CPU, such as the In 2006, the first systems supporting a Serial Peripheral Interface (SPI) appeared, and the BIOS flash moved again. Interface The SPI bus specifies four logic signals SCLK &mdash Serial Clock (output from master MOSI/SIMO &mdash Master Output Slave Input (output

EEPROM chips are advantageous because they can be easily updated by the user; hardware manufacturers frequently issue BIOS updates to upgrade their products, improve compatibility and remove bugs. A software bug (or just “bug” is an error flaw mistake Failure, fault or “undocumented feature” in a Computer program that prevents it However, this advantage had the risk that an improperly executed or aborted BIOS update could render the computer or device unusable. To avoid these situations, more recent BIOSes use a "boot block"; a portion of the BIOS which runs first and must be updated separately. This code verifies if the rest of the BIOS is intact (using hash checksums or other methods), before transferring control to it. A hash function is any well-defined procedure or mathematical function for turning some kind of Data into a relatively small integer, that may A checksum is a form of Redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space ( Telecommunications If the boot block detects any corruption in the main BIOS, it will typically warn the user that a recovery process must be initiated by booting from removable media (floppy, CD or USB memory) so the user can try flashing the BIOS again. In Computer storage, removable media refers to storage media which can be removed from its reader device conferring portability on the data it carries Some motherboards have a backup BIOS (sometimes referred to as DualBIOS boards) to recover from BIOS corruptions. A motherboard is the central or primary Printed circuit board (PCB making up a complex electronic system such as a modern Computer or Laptop In 2007, Gigabyte began offering motherboards with a QuadBIOS recovery feature. Gigabyte Technology ( is a Taiwan-based manufacturer of Computer hardware products best known for its Motherboards The company is publicly held and traded [4]

Due to the limitation on the number of times flash memory media can be flashed, a flash-based BIOS is vulnerable to "flash-burn" viruses that repeatedly write to the flash, permanently corrupting chip content. 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.

The size of the BIOS, and the capacities of the ROM, EEPROM and other media it may be stored on, has increased over time as new features have been added to the code; BIOS versions now exist with sizes up to 8 megabytes.

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. A floppy disk is an increasingly Obsolete data storage medium that is composed of a disk of thin flexible ("floppy" Magnetic storage medium encased 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. RAID — which stands for Redundant Array of Inexpensive Disks,or alternatively Redundant Array of Independent Disks (a less specific name and thus now the A Network card, Network Adapter, LAN Adapter or NIC (network interface card is a piece of Computer hardware designed to allow computers

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. An Option ROM typically consists of Firmware that is called by the system BIOS.

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

PC operating systems such as DOS, including all DOS-based versions of MS Windows, as well as bootloaders, may continue to make use of the BIOS to handle input and output. In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market However, other modern operating systems will interact with hardware devices directly by using their own device drivers to directly access the hardware. In computing a device driver or software driver is a Computer program allowing higher-level computer programs to interact with a Hardware device Occasionally these add-in BIOSs are still called by these operating systems, in order to carry out specific tasks such as preliminary device initialization.

To find these memory mapped expansion ROMs during the boot process, PC BIOS implementations scan real memory from 0xC0000 to 0xF0000 on 2 kibibyte boundaries looking for the ROM signature bytes of 55h followed by AAh (0xAA55). For a valid expansion ROM, its signature is immediately followed by a single byte indicating the number of 512-byte blocks it occupies in real memory. The BIOS then jumps to the offset located immediately after this size byte; at which point the expansion ROM code takes over, using the BIOS services to register interrupt vectors for use by post-boot applications and provide a user configuration interface, or display diagnostic information. An interrupt vector is the Memory address of an Interrupt handler, or an index into an array called an Interrupt vector table or dispatch table

There are many methods and utilities for dumping the contents of various motherboard BIOS and expansion ROMs. Under a Microsoft OS, DEBUG can be used to examine 64 KiB segments of memory and save the contents to a file. debug is a command in DOS, MS-DOS, OS/2 and Microsoft Windows which runs the program debug For UNIX systems the dd command can be used by a user with root privileges: "dd if=/dev/mem bs=1k skip=768 count=256 2>/dev/null | strings -n 8". dd is a common UNIX program whose primary purpose is the Low-level copying and conversion of raw Data.

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 BIOSes 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

Some operating systems, for example MS-DOS, rely on the BIOS to carry out most input/output tasks within the PC. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft. A variety of technical reasons makes it inefficient for some recent operating systems written for 32-bit CPUs such as Linux and Microsoft Windows to invoke the BIOS directly. The range of Integer values that can be stored in 32 bits is 0 through 4294967295 or −2147483648 through 2147483647 using Two's complement encoding Linux (commonly pronounced ˈlɪnəks Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. 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. Open Firmware, or OpenBoot in Sun Microsystems parlance is a standard defining the interfaces of a computer Firmware system formerly endorsed by the Forth is a structured, imperative, stack-based, computer Programming language and programming environment It is included with Sun's SPARC computers, IBM's RS/6000 line, and other PowerPC CHRP motherboards. The System p, formerly known as RS/6000, was IBM 's RISC / UNIX -based server and workstation product line Common Hardware Reference Platform ( CHRP) was a standard System architecture for PowerPC based computer systems published jointly by IBM Later x86-based personal computer operating systems, like Windows NT, use their own, native drivers which also makes it much easier to extend support to new hardware, while the 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 can take control of the hardware. In computing bootstrapping ("to pull oneself up by one's bootstraps" refers to techniques that allow a simple system to activate a more complicated system

There was a similar transition 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. The Macintosh Toolbox is a set of Application programming interfaces with a particular access mechanism These Apple ROMs were replaced by Open Firmware in the PowerPC Macintosh, then EFI in Intel Macintosh computers. PowerPC is a RISC Instruction set architecture created by the 1991 Apple – IBM – Motorola alliance known as AIM Macintosh, commonly nicknamed Mac is a Brand name which covers several lines of Personal computers designed developed and marketed by Apple Inc The Extensible Firmware Interface ( EFI) is a specification that defines a software Interface between an Operating system and platform Firmware

Later BIOS took on more complex functions, by way of interfaces such as ACPI; these functions include power management, hot swapping and thermal management. The Advanced Configuration and Power Interface ( ACPI) specification an open industry standard first released in December 1996 (developed by HP, Intel Power management is a feature of some electrical appliances especially copiers, computers and computer Peripherals such as monitors and Hot swapping and hot plugging are terms used to separately describe the functions of replacing system components hot swapping describes changing components like fans and However BIOS limitations (16-bit processor mode, only 1 MiB 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. The Extensible Firmware Interface ( EFI) is a specification that defines a software Interface between an Operating system and platform Firmware Initially written for the Itanium architecture, EFI is now available for x86 and x86-64 platforms; the specification development is driven by The Unified EFI Forum, an industry Special Interest Group. See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal x86-64 is a Superset of the x86 instruction set architecture. The Unified EFI Forum or UEFI Forum (where UEFI stands for Unified Extensible Firmware Interface) is an alliance between several leading technology companies including This article is about computer associations For political advocates see Interest group.

Linux has supported EFI via the elilo boot loader. elilo is the standard Linux Boot loader for EFI-based PC hardware 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 coreboot and OpenBIOS/Open Firmware projects. Coreboot (formerly known as LinuxBIOS is a Free software project endorsed by the Free Software Foundation, aimed at replacing the standard BIOS Firmware OpenBIOS is a project aiming to provide free and Open source implementations of Open Firmware. Open Firmware, or OpenBoot in Sun Microsystems parlance is a standard defining the interfaces of a computer Firmware system formerly endorsed by the AMD provided product specifications for some chipsets, and Google is sponsoring the project. Google Inc is an American public corporation, earning revenue from advertising related to its Internet search, e-mail, online Motherboard manufacturer Tyan offers coreboot next to the standard BIOS with their Opteron line of motherboards. A motherboard is the central or primary Printed circuit board (PCB making up a complex electronic system such as a modern Computer or Laptop Tyan Computer Corporation (also known as Tyan Business Unit or TBU is a subsidiary of MiTAC International and a manufacturer of computer Motherboards including Coreboot (formerly known as LinuxBIOS is a Free software project endorsed by the Free Software Foundation, aimed at replacing the standard BIOS Firmware The Opteron is AMD 's X86 server processor line and was the first processor to implement the AMD64 Instruction set architecture (known MSI and Gigabyte have followed suit with the MSI K9ND MS-9282 and MSI K9SD MS-9185 resp. Micro-Star International (MSI is a Computer hardware Manufacturer most well known for Desktop computer Motherboards Gigabyte Technology ( is a Taiwan-based manufacturer of Computer hardware products best known for its Motherboards The company is publicly held and traded 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), General Software, Insyde Software, and Phoenix Technologies (which bought Award Software International in 1998). American Megatrends Incorporated ( AMI) is a hardware and Software company headquartered in unincorporated Gwinnett County, Insyde Software ( is listed on the Gre Tai Market of Taiwan The company is headquartered in Taipei with offices in Westborough Massachusetts and Portland Oregon Phoenix Technologies Ltd ( is a creator of computer BIOS software Award Software International Inc was a BIOS manufacturer headquartered in Mountain View, California, United States.

See also

Sources

Notes and References

  1. ^ IBM Personal Computer Technical Reference manual, IBM Corporation, First Edition, Revised March 1983, page iii
  2. ^ Mukherjee, Anindya & Narushoff, Paul (1993), Programmer's Guide to the AMIBIOS, Windcreat/McGraw-Hill, ISBN 0-07-001561-9 
  3. ^ HowStuffWorks: What BIOS Does. The Advanced Configuration and Power Interface ( ACPI) specification an open industry standard first released in December 1996 (developed by HP, Intel ARCS is a Firmware Bootloader (also known as a PROM Console) used in most Computers produced by SGI since the beginning In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system BIOS Interrupt Calls are a facility that DOS programs and some other software such as Boot loaders use to invoke the BIOS 's facilities Coreboot (formerly known as LinuxBIOS is a Free software project endorsed by the Free Software Foundation, aimed at replacing the standard BIOS Firmware Free software or software libre is Software that can be used studied and modified without restriction and which can be copied and redistributed in modified or unmodified The Extensible Firmware Interface ( EFI) is a specification that defines a software Interface between an Operating system and platform Firmware In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. In X86 architecture, an input/output base address is a Base address used for an I/O port. Non-volatile BIOS memory refers to the memory on a Personal computer Motherboard containing BIOS settings and sometimes the code used to initialize Open Firmware, or OpenBoot in Sun Microsystems parlance is a standard defining the interfaces of a computer Firmware system formerly endorsed by the A real-time operating system ( RTOS; generally pronounced as "are-toss" is a multitasking Operating system intended for real-time POSIX (ˈpɒzɪks or "Portable Operating System Interface" is the collective name of a family of related standards specified by the IEEE to define Power-on self-test (POST is the common term for a computer router or printer's pre-boot sequence.
  4. ^ "Quad BIOS is a unique GIGABYTE feature that includes DualBIOS and Xpress BIOS Rescue Technology. This combination delivers a safety assurance mechanism that sports a total of 4 copies of BIOS distributed between the Flash ROM, hard-disk and driver CD. " Gigabyte Corporate News, January 15, 2007.
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