BIOS

The Basic Input/Output System, or BIOS, is a de facto standard that defines the Firmware interface for IBM PC compatible computers. It is also known as System BIOS, ROM BIOS, and PC BIOS. The name originated in 1975, in the BIOS used by the CP/M operating system.

The BIOS firmware is installed inside the personal computer (PC), and is the first program that runs when the computer is turned on.

The primary purpose of the BIOS is to boot, and test the system hardware and load a bootloader or operating system from a data storage device. In addition, the BIOS provides an abstraction layer for hardware, for example, consisting of a way for application programs and operating systems to interact with the keyboard, monitor, and other input devices. /exit. Variations that occur in the system hardware are hidden by the BIOS, since programs use BIOS services instead of directly accessing the hardware. Modern operating systems bypass the abstraction layer provided by the BIOS and access the hardware directly.

The original IBM PC/XT BIOS had no interactive user interface. Error messages were displayed on the screen, or encoded by means of a series of beeps. Options on the PC and XT were set via switches and jumpers on the motherboard and peripheral boards. Modern Wintel-compatible computers provide a configuration routine, accessible at system boot by a specific key sequence. The user can configure the system options using the keyboard and the monitor.

The BIOS software is stored in a non-volatile ROM chip on the motherboard. It is specifically designed to work with each particular computer model, interconnecting the various devices that make up the system's complementary chipset. In modern computers, the BIOS is stored on flash memory, so its contents can be rewritten without removing the integrated circuit from the motherboard. This makes the BIOS easy to update to add new features or fix bugs, but can make the computer vulnerable to BIOS rootkits.

MS-DOS (PC DOS) was the dominant PC operating system from the early 1980s to the mid-1990s. It relied on BIOS services for disk, keyboard, and text display functions. Windows NT, Linux, and other protected-mode operating systems generally do not use it after it is loaded into memory.

BIOS technology has been transitioning to Unified Extensible Firmware Interface (UEFI) since 2010.

History

/* C P / M B A S I C I / O S Y S T E M (B I O S)
COPYRIGHT (C) GARY A. KILDALL
JUNE, 1975 */
[...]
/* B A S I C D I S K O P E R A T I N G S Y S T E M (B D O S)
COPYRIGHT (C) GARY A. KILDALL
JUNE, 1975 */

The acronym BIOS was invented by Gary Kildall and first appeared in 1975 in the CP/M operating system describing the machine-specific part of the CP/M loaded at boot time. which interacts directly with the hardware (usually a CP/M machine just has a simple boot in its ROM).

The MS-DOS or PC DOS versions contain a file named by one of the following names: IO.SYS, IBMBIO.COM, IBMBIO.SYS, or DRBIOS.SYS. This file is known as the BIOS DOS or System I/O DOS, and contains the low-level hardware specific part of the operating system. Together with the hardware specific to, but independent of the underlying system BIOS the operating system residing in the ROM, this represents the analogue of the CP/M BIOS.

On other types of computers, the terms boot monitor, bootloader, and boot ROM are used instead. Some PowerPC and Sun based computers use Open Firmware for this purpose.

With the introduction of PS/2 machines, IBM divided the system BIOS into real-mode and protected-mode portions. The real mode portion was intended to provide backwards compatibility with operating systems such as DOS, and was therefore named CBIOS (for BIOS Compatibility), while the ABIOS (for Advanced BIOS) provided new interfaces specifically tailored for multitasking operating systems such as OS/2.

There are some alternatives to the legacy BIOS functionality in the x86 world: Extensible Firmware Interface, Open Firmware (used in the OLPC XO-1), and Coreboot.

Operation

When the x86 processor is rebooted, the program counter with a fixed address is loaded on top of the 1-megabyte real-mode address space. The BIOS memory address is located in such a way that it will run when the computer is first started up. Then, a jump instruction directs the processor to start executing code in the BIOS. If the system has just been powered on or the reset button has been pressed (cold boot), the power-on self-test (POST) is fully executed. If Ctrl+Alt+Del ("warm start"), special flag value detected in memory non-volatile (NVRAM) and the BIOS does not run the POST. This saves time otherwise used to discover and test all memory. NVRAM is on real time clock (RTC).

Self-diagnostic tests indicator, identifies and initializes system devices such as CPU, RAM, DMA controllers and switches, and other chipset parts, video card, keyboard, hard disk drive, optical disk drive and other basic hardware. The BIOS locates bootloader software held on a storage device designated as a boot device, such as a hard drive, floppy disk, CD, or DVD, loads, and runs that software >, giving you control of the PC. This process is known as a boot or boot sequence.

Firmware Update

For a motherboard reference, the manufacturer may release various BIOS revisions, which fix problems found in early batches, code better drivers, or support new processors.

The update of this firmware can be done with a program to burn a new version directly from the operating system, the programs are proprietary to each company that develops the firmware and they can usually be found on the internet along with the BIOS itself.

Updating the BIOS is perceived as not without risk, since a failure in the procedure leads to the motherboard not booting. Because of this, some manufacturers use systems such as the boot lock, which is a portion of the BIOS that is protected and not upgradable unlike the rest of the firmware.

Overclocking

Some BIOS chips allow overclocking, an action in which the CPU is set to a higher clock speed than its factory setting. In a proactive manner, it is highly recommended to implement a correct and reliable cooling and temperature control system that ensures the preservation of the structural integrity of the electronic components that will be affected by the action of overclocking, including the protection of components such as the bus, chips and multiple additional electronic devices, considering the proportionality rule described as the Joule Effect: "the amount of heat produced by a wire (electrical conductor) is proportional to the square of the current that passes through the wire conductor, multiplied by its electrical resistance." Overclocking could seriously compromise system reliability in undercooled computers and lead to reduced component life. If done correctly, overclocking can ensure the structural integrity and increased performance of the electronic components on the motherboard, otherwise it could cause the components to overheat and instantly self-destruct.

Firmware on adapter cards

A system can contain several chips with BIOS firmware in addition to the one on the motherboard: video cards, network cards, and others load chunks of code into memory (with the help of the main BIOS) that enables these devices to function.

The video BIOS is visible as a separate integrated one.

Video Cards

Unlike other system components, the video card must work from initial boot, long before any operating system is being loaded into RAM: on systems with integrated video, the motherboard BIOS contains the necessary routines to run the board's video.

Early computers (which did not have integrated video) had BIOSes capable of controlling any MDA and CGA adapter cards. In 1984 when new systems such as the EGA appeared, it was necessary to add a video BIOS to maintain compatibility with those systems that did not have the handling routines for the new standard; since then, video cards include their own firmware.

The BIOS of these adapters provides basic tools for managing the video hardware offered by the card. When the computer starts up, some of these cards display the card's brand, model, and firmware version as well as the size of the video memory.

The BIOS market

The vast majority of vendors of x86 architecture motherboards outsource the production of BIOSes to third parties. Manufacturers often write and release firmware updates that fix problems or add compatibility to new products.

The main providers of BIOSes are American Megatrends (AMI) and Phoenix Technologies (which bought Award Software International in 1998).

There are BIOS projects under the Free Software scheme, such as Coreboot, that offer alternative firmware for a few motherboard references.

Alternatives and successors

The Unified Extensible Firmware Interface (UEFI) supplements the BIOS on many new machines. Initially written for Intel Itanium Architecture, UEFI is now available for x86 and ARM architecture platforms; specification development is led by the Unified EFI Forum, an industry special interest group. EFI booting has only been supported on versions of Microsoft Windows that support the GUID Partition Table, Linux Kernel 2.6.1 and later, and macOS on Intel-based Macs. As of 2014, newer hardware PCs ship predominantly with UEFI firmware. The rootkit protection architecture can also prevent the system from executing user's own software changes, making UEFI controversial as a legacy BIOS replacement in the Free Hardware community. Also, Windows 11 requires UEFI to boot.