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75-558: Most of the implementations provided by OpenBIOS rely on additional lower-level firmware for hardware initialization, such as coreboot or Das U-Boot . Open Firmware implements the IEEE 1275-1994 standard. Open Firmware was released by the company Firmworks . The principal architect of Open Firmware, Mitch Bradley , is chairman of the Open Firmware Working Group and president and founder of Firmworks. The OLPC XO-1 laptop uses

150-562: A kernel . In the era of DOS , the BIOS provided BIOS interrupt calls 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. 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

225-463: A network adapter attempts booting by a procedure that is defined by its option ROM or the equivalent integrated into the motherboard BIOS ROM. As such, option ROMs may also influence or supplant the boot process defined by the motherboard BIOS ROM. With the El Torito optical media boot standard , the optical drive actually emulates a 3.5" high-density floppy disk to the BIOS for boot purposes. Reading

300-533: A BIOS upgrade that fails could brick the motherboard. Unified Extensible Firmware Interface (UEFI) is a successor to the legacy PC BIOS, aiming to address its technical limitations. UEFI firmware may include legacy BIOS compatibility to maintain compatibility with operating systems and option cards that do not support UEFI native operation. Since 2020, all PCs for Intel platforms no longer support Legacy BIOS. The last version of Microsoft Windows to officially support running on PCs which use legacy BIOS firmware

375-602: A ROM chip) that contains a BIOS extension ROM. The motherboard BIOS typically contains code for initializing and bootstrapping integrated display and integrated storage. The initialization process can involve the execution of code related to the device being initialized, for locating the device, verifying the type of device, then establishing base registers, setting pointers , establishing interrupt vector tables, selecting paging modes which are ways for organizing available registers in devices, setting default values for accessing software routines related to interrupts , and setting

450-516: A SLIC can be preactivated with an OEM product key, and they verify an XML formatted OEM certificate against the SLIC in the BIOS as a means of self-activating (see System Locked Preinstallation , SLP). If a user performs a fresh install of Windows, they will need to have possession of both the OEM key (either SLP or COA) and the digital certificate for their SLIC in order to bypass activation. This can be achieved if

525-425: A computer, exfiltrate data, or spy on the user. Other security researchers have worked further on how to exploit the principles behind BadUSB, releasing at the same time the source code of hacking tools that can be used to modify the behavior of different USB devices. BIOS In computing , BIOS ( / ˈ b aɪ ɒ s , - oʊ s / , BY -oss, -⁠ohss ; Basic Input/Output System , also known as

600-417: A consistent environment necessary for running more complex programs at the user's discretion. This required programming the computer to run those programs automatically. Furthermore, as companies, universities, and marketers wanted to sell computers to laypeople with little technical knowledge, greater automation became necessary to allow a lay-user to easily run programs for practical purposes. This gave rise to

675-608: A hard disk that is bootable, but sometimes there is a removable-media drive that has higher boot priority, so the user can cause a removable disk to be booted. In most modern BIOSes, the boot priority order can be configured by the user. In older BIOSes, limited boot priority options are selectable; in the earliest BIOSes, a fixed priority scheme was implemented, with floppy disk drives first, fixed disks (i.e., hard disks) second, and typically no other boot devices supported, subject to modification of these rules by installed option ROMs. The BIOS in an early PC also usually would only boot from

750-445: A kind of software that a user would not consciously run, and it led to software that a lay user wouldn't even know about. As originally used, firmware contrasted with hardware (the CPU itself) and software (normal instructions executing on a CPU). It was not composed of CPU machine instructions, but of lower-level microcode involved in the implementation of machine instructions. It existed on

825-512: A message like "No bootable disk found"; some would prompt for a disk to be inserted and a key to be pressed to retry the boot process. A modern BIOS may display nothing or may automatically enter the BIOS configuration utility when the boot process fails. The environment for the boot program is very simple: the CPU is in real mode and the general-purpose and segment registers are undefined, except SS, SP, CS, and DL. CS:IP always points to physical address 0x07C00 . What values CS and IP actually have

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900-409: A more complex device, firmware may provide relatively low-level control as well as hardware abstraction services to higher-level software such as an operating system . Firmware is found in a wide range of computing devices including personal computers , phones , home appliances , vehicles , computer peripherals and in many of the digital chips inside each of these larger systems. Firmware

975-532: A network device or a SCSI adapter) in a cooperative way, 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

1050-422: A portion of the " upper memory area " (the part of the x86 real-mode address space at and above address 0xA0000) and runs each ROM found, in order. To discover memory-mapped option ROMs, a BIOS implementation scans the real-mode address space from 0x0C0000 to 0x0F0000 on 2  KB (2,048 bytes) boundaries, looking for a two-byte ROM signature : 0x55 followed by 0xAA. In a valid expansion ROM, this signature

1125-441: A program from the provider, and will often allow the old firmware to be saved before upgrading so it can be reverted to if the process fails, or if the newer version performs worse. Free software replacements for vendor flashing tools have been developed, such as Flashrom . Sometimes, third parties develop an unofficial new or modified ("aftermarket") version of firmware to provide new features or to unlock hidden functionality; this

1200-460: A reserved block of system RAM at addresses 0x00400–0x004FF with various parameters initialized during the POST. All memory at and above address 0x00500 can be used by the boot program; it may even overwrite itself. The BIOS ROM is customized to the particular manufacturer's hardware, allowing low-level services (such as reading a keystroke or writing a sector of data to diskette) to be provided in

1275-500: A simple boot loader in its ROM.) Versions of MS-DOS , PC DOS or DR-DOS contain a file called variously " IO.SYS ", " IBMBIO.COM ", "IBMBIO.SYS", or "DRBIOS.SYS"; this file is known as the "DOS BIOS" (also known as the "DOS I/O System") and contains the lower-level hardware-specific part of the operating system. Together with the underlying hardware-specific but operating system-independent "System BIOS", which resides in ROM , it represents

1350-607: A software licensing description table (SLIC), a digital signature placed inside the BIOS by the original equipment manufacturer (OEM), for example Dell . The SLIC is inserted into the ACPI data table and contains no active code. Computer manufacturers that distribute OEM versions of Microsoft Windows and Microsoft application software can use the SLIC to authenticate licensing to the OEM Windows Installation disk and system recovery disc containing Windows software. Systems with

1425-454: A standardized way to programs, including operating systems. For example, an IBM PC might have either a monochrome or a color display adapter (using different display memory addresses and hardware), but a single, standard, BIOS system call may be invoked to display a character at a specified position on the screen in text mode or graphics mode . The BIOS provides a small library of basic input/output functions to operate peripherals (such as

1500-472: Is Windows 10 as Windows 11 requires a UEFI-compliant system (except for IoT Enterprise editions of Windows 11 since version 24H2 ). The term BIOS (Basic Input/Output System) was created by Gary Kildall and first appeared in the CP/M operating system in 1975, describing the machine-specific part of CP/M loaded during boot time that interfaces directly with the hardware . (A CP/M machine usually has only

1575-658: Is a major threat to system security: "Your biggest mistake is to assume that the NSA is the only institution abusing this position of trust – in fact, it's reasonable to assume that all firmware is a cesspool of insecurity, courtesy of incompetence of the highest degree from manufacturers, and competence of the highest degree from a very wide range of such agencies". As a potential solution to this problem, he has called for declarative firmware, which would describe "hardware linkage and dependencies" and "should not include executable code ". Firmware should be open-source so that

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1650-406: Is bootable by attempting to load the first sector ( boot sector ). If the sector cannot be read, the BIOS proceeds to the next device. If the sector is read successfully, some BIOSes will also check for the boot sector signature 0x55 0xAA in the last two bytes of the sector (which is 512 bytes long), before accepting a boot sector and considering the device bootable. When a bootable device is found,

1725-449: Is followed by a single byte indicating the number of 512-byte blocks the expansion ROM occupies in real memory, and the next byte is the option ROM's entry point (also known as its "entry offset"). If the ROM has a valid checksum, the BIOS transfers control to the entry address, which in a normal BIOS extension ROM should be the beginning of the extension's initialization routine. At this point,

1800-434: Is less frequently updated, even when flash memory (rather than ROM, EEPROM) storage is used for the firmware. Most computer peripherals are themselves special-purpose computers. Devices such as printers, scanners, webcams, and USB flash drives have internally-stored firmware; some devices may also permit field upgrading of their firmware. For modern simpler devices, such as USB keyboards , USB mouses and USB sound cards ,

1875-556: Is not well defined. Some BIOSes use a CS:IP of 0x0000:0x7C00 while others may use 0x07C0:0x0000 . Because boot programs are always loaded at this fixed address, there is no need for a boot program to be relocatable. DL may contain the drive number, as used with interrupt 13h , of the boot device. SS:SP points to a valid stack that is presumably large enough to support hardware interrupts, but otherwise SS and SP are undefined. (A stack must be already set up in order for interrupts to be serviced, and interrupts must be enabled in order for

1950-465: Is performed each time the system is powered up. Without reprogrammable microcode, an expensive processor swap would be required; for example, the Pentium FDIV bug became an expensive fiasco for Intel as it required a product recall because the original Pentium processor's defective microcode could not be reprogrammed. Operating systems can update main processor microcode also. Some BIOSes contain

2025-607: Is portable and licensed under the GPL . It is produced by the OpenBIOS project. Slimline Open Firmware is produced by IBM , and is released under a BSD style license. It supports the PowerPC architecture. Firmware In computing , firmware is software that provides low-level control of computing device hardware . For a relatively simple device, firmware may perform all control, monitoring and data manipulation functionality. For

2100-530: Is rebooting. When interrupt 19h is called, the BIOS attempts to locate boot loader software on a "boot device", such as a hard disk , a floppy disk , CD , or DVD . It loads and executes the first boot software it finds, giving it control of the PC. The BIOS uses the boot devices set in Nonvolatile BIOS memory ( CMOS ), or, in the earliest PCs, DIP switches . The BIOS checks each device in order to see if it

2175-471: Is referred to as custom firmware . An example is Rockbox as a firmware replacement for portable media players . There are many homebrew projects for various devices, which often unlock general-purpose computing functionality in previously limited devices (e.g., running Doom on iPods ). Firmware hacks usually take advantage of the firmware update facility on many devices to install or run themselves. Some, however, must resort to exploits to run, because

2250-480: Is running. The interrupt vectors corresponding to the BIOS interrupts have been set to point at the appropriate entry points in the BIOS, hardware interrupt vectors for devices initialized by the BIOS have been set to point to the BIOS-provided ISRs, and some other interrupts, including ones that BIOS generates for programs to hook, have been set to a default dummy ISR that immediately returns. The BIOS maintains

2325-494: Is stored in non-volatile memory – either read-only memory (ROM) or programmable memory such as EPROM , EEPROM , or flash . Changing a device's firmware stored in ROM requires physically replacing the memory chip – although some chips are not designed to be removed after manufacture. Programmable firmware memory can be reprogrammed via a procedure sometimes called flashing . Common reasons for changing firmware include fixing bugs and adding features . Ascher Opler used

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2400-663: Is unique among PCs in having two ROM cartridge slots on the front. Cartridges in these slots map into the same region of the upper memory area used for option ROMs, and the cartridges can contain option ROM modules that the BIOS would recognize. The cartridges can also contain other types of ROM modules, such as BASIC programs, that are handled differently. One PCjr cartridge can contain several ROM modules of different types, possibly stored together in one ROM chip. The 8086 and 8088 start at physical address FFFF0h. The 80286 starts at physical address FFFFF0h. The 80386 and later x86 processors start at physical address FFFFFFF0h. When

2475-608: The CPU , chipset , RAM , motherboard , video card , keyboard , mouse , hard disk drive , optical disc drive and other hardware , including integrated peripherals . Early IBM PCs had a routine in the POST that would download a program into RAM through the keyboard port and run it. This feature was intended for factory test or diagnostic purposes. After the motherboard BIOS completes its POST, most BIOS versions search for option ROM modules, also called BIOS extension ROMs, and execute them. The motherboard BIOS scans for extension ROMs in

2550-541: The System BIOS , ROM BIOS , BIOS ROM or PC BIOS ) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process (power-on startup). The firmware comes pre-installed on the computer's motherboard . The name originates from the Basic Input/Output System used in the CP/M operating system in 1975. The BIOS firmware

2625-423: The "first sector" of a CD-ROM or DVD-ROM is not a simply defined operation like it is on a floppy disk or a hard disk. Furthermore, the complexity of the medium makes it difficult to write a useful boot program in one sector. The bootable virtual floppy disk can contain software that provides access to the optical medium in its native format. If an expansion ROM wishes to change the way the system boots (such as from

2700-430: The 1980s under MS-DOS , when programmers observed that using the BIOS video services for graphics display were very slow. To increase the speed of screen output, many programs bypassed the BIOS and programmed the video display hardware directly. Other graphics programmers, particularly but not exclusively in the demoscene , observed that there were technical capabilities of the PC display adapters that were not supported by

2775-424: The BIOS after completing its initialization process. Once (and if) an option ROM returns, the BIOS continues searching for more option ROMs, calling each as it is found, until the entire option ROM area in the memory space has been scanned. It is possible that an option ROM will not return to BIOS, pre-empting the BIOS's boot sequence altogether. After the POST completes and, in a BIOS that supports option ROMs, after

2850-601: The BIOS to carry out most input/output tasks within the PC. Calling real mode BIOS services directly is inefficient for protected mode (and long mode ) operating systems. BIOS interrupt calls are not used by modern multitasking operating systems after they initially load. In the 1990s, BIOS provided some protected mode interfaces for Microsoft Windows and Unix-like operating systems, such as Advanced Power Management (APM), Plug and Play BIOS , Desktop Management Interface (DMI), VESA BIOS Extensions (VBE), e820 and MultiProcessor Specification (MPS). Starting from

2925-408: The BIOS transfers control to the loaded sector. The BIOS does not interpret the contents of the boot sector other than to possibly check for the boot sector signature in the last two bytes. Interpretation of data structures like partition tables and BIOS Parameter Blocks is done by the boot program in the boot sector itself or by other programs loaded through the boot process. A non-disk device such as

3000-630: The BIOS. Code in option ROMs runs before the BIOS boots the operating system from mass storage . These ROMs typically test and initialize hardware, add new BIOS services, or replace existing BIOS services with their own services. For example, a SCSI controller usually has a BIOS extension ROM that adds support for hard drives connected through that controller. An extension ROM could in principle contain operating system, or it could implement an entirely different boot process such as network booting . Operation of an IBM-compatible computer system can be completely changed by removing or inserting an adapter card (or

3075-556: The Equation Group in at least 42 countries. Mark Shuttleworth , the founder of the company Canonical , which created the Ubuntu Linux distribution, has described proprietary firmware as a security risk, saying that "firmware on your device is the NSA 's best friend" and calling firmware "a trojan horse of monumental proportions". He has asserted that low-quality, closed source firmware

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3150-713: The GUI or even the battery life. Smartphones have a firmware over the air upgrade capability for adding new features and patching security issues. Since 1996, most automobiles have employed an on-board computer and various sensors to detect mechanical problems. As of 2010 , modern vehicles also employ computer-controlled anti-lock braking systems (ABS) and computer-operated transmission control units (TCUs). The driver can also get in-dash information while driving in this manner, such as real-time fuel economy and tire pressure readings. Local dealers can update most vehicle firmware. Other firmware applications include: Flashing involves

3225-696: The IBM BIOS and could not be taken advantage of without circumventing it. Since the AT-compatible BIOS ran in Intel real mode , operating systems that ran in protected mode on 286 and later processors required hardware device drivers compatible with protected mode operation to replace BIOS services. In modern PCs running modern operating systems (such as Windows and Linux ) the BIOS interrupt calls are used only during booting and initial loading of operating systems. Before

3300-524: The Open Firmware implementation. It supports the x86 , PowerPC , and ARM architectures, and is released under the terms of a BSD style license. SmartFirmware includes a C to FCode compiler. It is made by CodeGen, Inc. It is written in ANSI C and supports the x86 , PowerPC , SPARC , ARM , MIPS architectures. OpenBOOT was released by Sun Microsystems . It supports the sun4v architecture. OpenBIOS

3375-542: The analogue to the " CP/M BIOS ". The BIOS originally proprietary to the IBM PC has been reverse engineered by some companies (such as Phoenix Technologies ) looking to create compatible systems. With the introduction of PS/2 machines, IBM divided the System BIOS into real- and protected-mode portions. The real-mode portion was meant to provide backward compatibility with existing operating systems such as DOS, and therefore

3450-500: The boot sequence by inserting its own boot actions into it, by preventing the BIOS from detecting certain devices as bootable, or both. Before the BIOS Boot Specification was promulgated, this was the only way for expansion ROMs to implement boot capability for devices not supported for booting by the native BIOS of the motherboard. The user can select the boot priority implemented by the BIOS. For example, most computers have

3525-400: The boundary between hardware and software; thus the name firmware . Over time, popular usage extended the word firmware to denote any computer program that is tightly linked to hardware, including BIOS on PCs, boot firmware on smartphones, computer peripherals , or the control systems on simple consumer electronic devices such as microwave ovens , remote controls . In some respects,

3600-454: The card is not supported by the motherboard BIOS and the card needs to be initialized or made accessible through BIOS services before the operating system can be loaded (usually this means it is required in the boot process). An additional advantage of ROM on some early PC systems (notably including the IBM PCjr) was that ROM was faster than main system RAM. (On modern systems, the case is very much

3675-592: The code can be checked and verified. Custom firmware hacks have also focused on injecting malware into devices such as smartphones or USB devices . One such smartphone injection was demonstrated on the Symbian OS at MalCon , a hacker convention . A USB device firmware hack called BadUSB was presented at the Black Hat USA 2014 conference, demonstrating how a USB flash drive microcontroller can be reprogrammed to spoof various other device types to take control of

3750-484: The computer, and if it was lost the system settings could not be changed. The same applied in general to computers with an EISA bus, for which the configuration program was called an EISA Configuration Utility (ECU). A modern Wintel -compatible computer provides a setup routine essentially unchanged in nature from the ROM-resident BIOS setup utilities of the late 1990s; the user can configure hardware options using

3825-440: The device's configuration using default values. In addition, plug-in adapter cards such as SCSI , RAID , network interface cards , and video cards often include their own BIOS (e.g. Video BIOS ), complementing or replacing the system BIOS code for the given component. Even devices built into the motherboard can behave in this way; their option ROMs can be a part of the motherboard BIOS. An add-in card requires an option ROM if

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3900-606: The drive is formatted or wiped. Although the Kaspersky Lab report did not explicitly claim that this group is part of the United States National Security Agency (NSA), evidence obtained from the code of various Equation Group software suggests that they are part of the NSA. Researchers from the Kaspersky Lab categorized the undertakings by Equation Group as the most advanced hacking operation ever uncovered, also documenting around 500 infections caused by

3975-480: The expansion ROMs have finished executing and registering themselves with the BBS API. Also, if an expansion ROM wishes to change the way the system boots unilaterally, it can simply hook interrupt 19h or other interrupts normally called from interrupt 19h, such as interrupt 13h, the BIOS disk service, to intercept the BIOS boot process. Then it can replace the BIOS boot process with one of its own, or it can merely modify

4050-416: The extension ROM code takes over, typically testing and initializing the hardware it controls and registering interrupt vectors for use by post-boot applications. It may use BIOS services (including those provided by previously initialized option ROMs) to provide a user configuration interface, to display diagnostic information, or to do anything else that it requires. An option ROM should normally return to

4125-465: The first floppy disk drive or the first hard disk drive, even if there were two drives installed. On the original IBM PC and XT, if no bootable disk was found, the BIOS would try to start ROM BASIC with the interrupt call to interrupt 18h . Since few programs used BASIC in ROM, clone PC makers left it out; then a computer that failed to boot from a disk would display "No ROM BASIC" and halt (in response to interrupt 18h). Later computers would display

4200-403: The keyboard and video display. The modern Wintel machine may store the BIOS configuration settings in flash ROM, perhaps the same flash ROM that holds the BIOS itself. Peripheral cards such as hard disk drive host bus adapters and video cards have their own firmware, and BIOS extension option ROM code may be a part of the expansion card firmware; that code provides additional capabilities in

4275-654: The keyboard, rudimentary text and graphics display functions and so forth). When using MS-DOS, BIOS services could be accessed by an application program (or by MS-DOS) by executing an interrupt 13h interrupt instruction to access disk functions, or by executing one of a number of other documented BIOS interrupt calls to access video display , keyboard , cassette, and other device functions. Operating systems and executive software that are designed to supersede this basic firmware functionality provide replacement software interfaces to application software. Applications can also provide these services to themselves. This began even in

4350-446: The manufacturer has attempted to lock the hardware to stop it from running unlicensed code . Most firmware hacks are free software . The Moscow-based Kaspersky Lab discovered that a group of developers it refers to as the " Equation Group " has developed hard disk drive firmware modifications for various drive models, containing a trojan horse that allows data to be stored on the drive in locations that will not be erased even if

4425-527: The operating system's first graphical screen is displayed, input and output are typically handled through BIOS. A boot menu such as the textual menu of Windows, which allows users to choose an operating system to boot, to boot into the safe mode , or to use the last known good configuration, is displayed through BIOS and receives keyboard input through BIOS. Many modern PCs can still boot and run legacy operating systems such as MS-DOS or DR-DOS that rely heavily on BIOS for their console and disk I/O, providing that

4500-425: The option ROM scan is completed and all detected ROM modules with valid checksums have been called, the BIOS calls interrupt 19h to start boot processing. Post-boot, programs loaded can also call interrupt 19h to reboot the system, but they must be careful to disable interrupts and other asynchronous hardware processes that may interfere with the BIOS rebooting process, or else the system may hang or crash while it

4575-463: The overwriting of existing firmware or data, contained in EEPROM or flash memory module present in an electronic device, with new data. This can be done to upgrade a device or to change the provider of a service associated with the function of the device, such as changing from one mobile phone service provider to another or installing a new operating system. If firmware is upgradable, it is often done via

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4650-539: The point of successfully initializing a video display adapter. Options on the IBM PC and XT were set by switches and jumpers on the main board and on expansion cards . Starting around the mid-1990s, it became typical for the BIOS ROM to include a "BIOS configuration utility" (BCU ) or "BIOS setup utility", accessed at system power-up by a particular key sequence. This program allowed the user to set system configuration options, of

4725-610: The reverse of this, and BIOS ROM code is usually copied ("shadowed") into RAM so it will run faster.) Option ROMs normally reside on adapter cards. However, the original PC, and perhaps also the PC XT, have a spare ROM socket on the motherboard (the "system board" in IBM's terms) into which an option ROM can be inserted, and the four ROMs that contain the BASIC interpreter can also be removed and replaced with custom ROMs which can be option ROMs. The IBM PCjr

4800-672: The stack set up by BIOS is unknown and its location is likewise variable; although the boot program can investigate the default stack by examining SS:SP, it is easier and shorter to just unconditionally set up a new stack. At boot time, all BIOS services are available, and the memory below address 0x00400 contains the interrupt vector table . BIOS POST has initialized the system timers, interrupt controller(s), DMA controller(s), and other motherboard/chipset hardware as necessary to bring all BIOS services to ready status. DRAM refresh for all system DRAM in conventional memory and extended memory, but not necessarily expanded memory, has been set up and

4875-531: The system has a BIOS, or a CSM-capable UEFI firmware. Intel processors have reprogrammable microcode since the P6 microarchitecture. AMD processors have reprogrammable microcode since the K7 microarchitecture. The BIOS contain patches to the processor microcode that fix errors in the initial processor microcode; microcode is loaded into processor's SRAM so reprogramming is not persistent, thus loading of microcode updates

4950-479: The system is initialized, the first instruction of the BIOS appears at that address. If the system has just been powered up or the reset button was pressed (" cold boot "), the full power-on self-test (POST) is run. If Ctrl+Alt+Delete was pressed (" warm boot "), a special flag value stored in nonvolatile BIOS memory (" CMOS ") tested by the BIOS allows bypass of the lengthy POST and memory detection. The POST identifies, tests and initializes system devices such as

5025-405: The system timer-tick interrupt, which BIOS always uses at least to maintain the time-of-day count and which it initializes during POST, to be active and for the keyboard to work. The keyboard works even if the BIOS keyboard service is not called; keystrokes are received and placed in the 15-character type-ahead buffer maintained by BIOS.) The boot program must set up its own stack, because the size of

5100-592: The term firmware in a 1967 Datamation article, as an intermediary term between "hardware" and "software". Opler projected that fourth-generation computer systems would have a writable control store (a small specialized high-speed memory) into which microcode firmware would be loaded. Many software functions would be moved to microcode, and instruction sets could be customized, with different firmware loaded for different instruction sets. As computers began to increase in complexity, it became clear that various programs needed to first be initiated and run to provide

5175-444: The trend is to store the firmware in on-chip memory in the device's microcontroller , as opposed to storing it in a separate EEPROM chip. Examples of computer firmware include: Consumer appliances like gaming consoles , digital cameras and portable music players support firmware upgrades. Some companies use firmware updates to add new playable file formats ( codecs ). Other features that may change with firmware updates include

5250-457: The type formerly set using DIP switches , through an interactive menu system controlled through the keyboard. In the interim period, IBM-compatible PCs‍—‌including the IBM AT ‍—‌held configuration settings in battery-backed RAM and used a bootable configuration program on floppy disk, not in the ROM, to set the configuration options contained in this memory. The floppy disk was supplied with

5325-777: The user performs a restore using a pre-customised image provided by the OEM. Power users can copy the necessary certificate files from the OEM image, decode the SLP product key, then perform SLP activation manually. Some BIOS implementations allow overclocking , an action in which the CPU is adjusted to a higher clock rate than its manufacturer rating for guaranteed capability. Overclocking may, however, seriously compromise system reliability in insufficiently cooled computers and generally shorten component lifespan. Overclocking, when incorrectly performed, may also cause components to overheat so quickly that they mechanically destroy themselves. Some older operating systems , for example MS-DOS , rely on

5400-502: The various firmware components are as important as the operating system in a working computer. However, unlike most modern operating systems, firmware rarely has a well-evolved automatic mechanism of updating itself to fix any functionality issues detected after shipping the unit. A computer's firmware may be manually updated by a user via a small utility program. In contrast, firmware in mass storage devices (hard-disk drives, optical disc drives, flash memory storage e.g. solid state drive)

5475-433: Was named "CBIOS" (for "Compatibility BIOS"), whereas the "ABIOS" (for "Advanced BIOS") provided new interfaces specifically suited for multitasking operating systems such as OS/2 . The BIOS of the original IBM PC and XT had no interactive user interface. Error codes or messages were displayed on the screen, or coded series of sounds were generated to signal errors when the power-on self-test (POST) had not proceeded to

5550-432: Was originally proprietary to the IBM PC ; it was reverse engineered by some companies (such as Phoenix Technologies ) looking to create compatible systems. The interface of that original system serves as a 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

5625-406: Was stored in a 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 rootkits . Furthermore,

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