If none was available, then the computer would perform tasks from other memory stores or display an error message, depending on the model and design of the computer and version of the BIOS.

If all else fails, it should issue an INT 18h BIOS interrupt call ( followed by an INT 19h just in case INT 18h would return ) in order to give back control to the BIOS, which would then attempt to boot off other devices, attempt a remote boot via network or invoke ROM BASIC.

The company could not copy the BIOS directly as a result of the court decision in Apple v. Franklin, but it could reverse-engineer the IBM BIOS and then write its own BIOS using clean room design.

For example, if the second or third hard disk is of SCSI type and on MS-DOS requires drivers loaded through the CONFIG. SYS file ( e. g. the controller card does not offer on-board BIOS or using this BIOS is not practical ), then the first SCSI primary partition will appear after all the IDE partitions on MS-DOS.

This mode-switching technique is also the one used by DPMI ( under real, not emulated, DOS ) and DOS extenders like DOS / 4GW to allow protected mode programs to run under DOS ; the DPMI system or DOS extender switches to real mode to invoke DOS or BIOS calls, then switches back to return to the application program which runs in protected mode.

On an IBM PC compatible machine, the BIOS selects a boot device, then copies the first sector from the device ( which may be a MBR, VBR or any executable code ), into physical memory at memory address 0x7C00.

If your computer is not booting from the device you desire, such as the floppy drive, you may have to enter the BIOS setup function by pressing a special key when the computer is first turned on ( such as Delete, F1, F2, F10 or F12 ), and then changing the boot order.

CIH filled the first 1024 KB of the host's boot drive with zeros and then attacked certain types of BIOS.

However, it is more convenient to have a multi-booting boot loader on one of the drives, set BIOS once to always start booting from ( i. e., load the boot loader from ) that drive, and then allow the user to choose an operating system from that boot loader's menu.

On Windows Vista and Windows 7, this can be fixed by setting non-AHCI mode in the BIOS then booting and changing the registry, then changing the BIOS setting to AHCI.

A BIOS interrupt handler would then translate the program's request to match the hardware that was actually present.

This provided a more standardized approach where an option ROM could be initialized at the start of the boot process, it could inform the BIOS about its functionality, and then it could be called later on in the boot process depending on the order the user had selected.

The term remains in wide use but it has grown into a misnomer: nonvolatile storage in contemporary computers is often in EEPROM or flash memory ( like the BIOS code itself ); the remaining usage for the battery is then to keep the real-time clock going.

If the x86 processor supports this feature in hardware, and if the system's BIOS provides support for this feature and it has been enabled, either by the manufacturer or the user, then the NX features are turned on in Windows, on a limited " OptIn " basis.

A software engineer was hired to write the special " dual boot mode " BIOS and the special CP / M BIOS.

The " dual boot mode " BIOS actually discovered whether a TRS-DOS, or Aster CP / M disk was placed in the drive, and would, depending on the type of disk, reorganise the internal memory architecture of the system, to either be 100 % TRS-80 compatible or optimally support CP / M, with as much " workspace " as possible, and the 80x25 video mode.

The name originated from the Basic Input Output System used in the CP / M operating system ( released in 1976 ), where the BIOS was loaded from disk, with only a small boot loader program stored in read-only memory.

The BIOS software is built into the PC, and is the first code run by a PC when powered on (' boot firmware ').

The term BIOS ( Basic Input / Output System ) was invented 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 a simple boot loader in its ROM ).

The first stage of boot loaders located on fixed disks and removable drives must fit into the first 446 bytes of the Master Boot Record in order to leave room for the default 64-byte partition table with four partition entries and the two-byte boot signature, which the BIOS requires for a proper boot loader — or even less, when additional features like more than four partition entries ( up to 16 with 16 bytes each ), a disk signature ( 6 bytes ), a disk timestamp ( 6 bytes ), an Advanced Active Partition ( 18 bytes ) or special multi-boot loaders If an active partition is found, the MBR code loads the boot sector code from that partition, known as Volume Boot Record ( VBR ), and executes it.

Also coreboot allows a computer to boot without having the firmware / BIOS constantly running in system management mode.

However, most boot loaders retain 16-bit support BIOS call support.

Once installed, the operating system ( BIOS, BDOS and CCP ) was stored in reserved areas at the beginning of any disk which would be used to boot the system.

VBE is made available through the video card's BIOS, which installs during boot up some interrupt vectors that point to itself.

There are also optimizations to prevent boot slowdown due to BIOS POST operations.

This led to boot failures whereby an older BIOS would not recognize a newer card, causing an error at startup.

This nonvolatile BIOS memory, often called CMOS RAM or parameter RAM, was a common solution in earlier computer systems like the original Apple Macintosh, which used a small amount of memory powered by a watch " button " battery for storing basic setup information like the selected boot volume.

The boot program loader and significant parts of the BIOS were stored in a 4 kilobyte EPROM, which was bank-switched.

The system console, computer console, root console, operator's console, or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the kernel, from the init system and from the system logger.

In this case a multi-booting boot loader is not strictly necessary because the user can choose to enter BIOS configuration immediately after power-up and make the desired drive first in the boot-order list.

Booting often involves processes such as perform self-tests, load configuration settings, loading a BIOS, resident monitors, a hypervisor, an operating system, or utility software.

BIOS software is stored on a non-volatile ROM chip on the motherboard.

In modern computer systems, the BIOS chip's contents can be rewritten without removing it from the motherboard, allowing BIOS software to be upgraded in place.

The BIOS provides a small library of basic input / output functions used to operate and control the peripherals ( such as the keyboard, text display functions and so forth ), and these software library functions are callable by external software.

A special BIOS routine — software interrupt 0x15, subfunction 0x85 — was added to signal the OS when SysRq was pushed or released.

Other problems can affect the ability to start or control the machine remotely: hardware failure of the machine or network, failure of the BIOS settings battery ( the machine will halt when started before the network connection is made, displaying an error message and requiring a keypress ), loss of control of the machine due to software problems ( machine hang, termination of remote control or networking software, etc.

In many desktop computers, for example, the bootstrapping process begins with the CPU executing software contained in ROM ( for example, the BIOS of an IBM PC ) at a predefined address ( some CPUs, including the Intel x86 series are designed to execute this software after reset without outside help ).

Firmware such as the ROM BIOS of a personal computer may contain only elementary basic functions of a device and may only provide services to higher-level software.

* Communications software directly accessed the UART serial port chip, because the MS-DOS API and the BIOS did not provide full support and was too slow to keep up with hardware which could transfer data at 19200 bit / s.

Physical and / or root-level access is required to the machine, and the software loaded into the BIOS needs to be created for the specific hardware that it will be running on.

VESA BIOS Extensions ( VBE ) is a VESA standard, currently at version 3, that defines the interface that can be used by software to access compliant video boards at high resolutions and bit depths.

For these reasons, software that relies on the BIOS and operating system to communicate with the hard drive is often unsuccessful in data recovery imaging ; separate hardware control of the source hard drive is required to achieve the full spectrum of data recovery imaging.

The video BIOS or firmware contains the basic program, which is usually hidden, that governs the video card's operations and provides the instructions that allow the computer and software to interact with the card.

Many newer motherboards support Pulse-width modulation ( PWM ) control, allowing the fan speed to be set in the BIOS or with software.

Generally only system software, i. e. the BIOS, operating systems, and some specialized utility programs ( e. g., memory testers ), address physical memory using machine code operands or processor registers, instructing the CPU to direct a hardware device, called the memory controller, to use the memory bus or system bus, or separate control, address and data busses, to execute the program's commands.

An overview of late 2011 usages of UEFI by independent hardware, BIOS, and software vendors.