Created By:Shikha Yadav | Created Date :14 March, 2023
In computers, BIOS(Basic Input Output System) (also known as system BIOS, ROM-BIOS, ROM-BIOS, or PC-BIOS) is firmware used to provide run-time services for operating systems and programs, and to perform hardware initialization during the boot process. BIOS firmware is pre-installed on an IBM PC or IBM PC-compatible system board and is present on some UEFI-based systems to maintain compatibility with operating systems that do not support native UEFI operation. The name comes from the Basic Input/Output System used in the CP/M operating system in 1975. Some companies (e.g. Phoenix Technologies) wanting to create compatible systems have reverse engineered the BIOS originally proprietary to the IBM PC. The interface of this original system serves as the de facto standard.
The BIOS in modern PCs initializes and tests the system's hardware components (power-on self-test) and loads a boot loader from a mass storage device, which then initializes a kernel. In the DOS era, the BIOS provided BIOS interrupt calls for the keyboard, display, memory, and other input/output (I/O) devices, standardizing an interface for application programs and the operating system. Newer operating systems do not use BIOS interrupt calls after boot.
Most BIOS implementations are specifically designed to work with a specific computer or motherboard model by interfacing with various devices, particularly the system chipset. Originally, the BIOS firmware was stored on a ROM chip on the PC's motherboard. In newer computer systems, the BIOS contents are stored in flash memory, so it can be rewritten without removing the chip from the motherboard. This allows for easy end-user updates of the BIOS firmware, adding new features or fixing bugs, but it also creates the possibility of the computer becoming infected with BIOS rootkits. Also, a failed BIOS update could damage the motherboard. The latest version of Microsoft Windows running on PCs with BIOS firmware is Windows 10.
The term BIOS (Basic Input/Output System) was developed by Gary Kildall and first appeared in the CP/M operating system in 1975. It describes the machine-specific part of CP/M that is loaded at boot and interacts directly with the hardware. (A CP/M machine usually only has a simple boot loader in its ROM.)
Versions of MS-DOS, PC DOS, or DR-DOS include a file named "IO.SYS", "IBMBIO.COM", "IBMBIO.SYS", or "DRBIOS.SYS"; This file is known as the "DOS BIOS. Together with the underlying hardware-specific, but operating system-independent "System-BIOS", which is located in the ROM, it represents the analogue of the "CP/M-BIOS".
With the introduction of PS/2 computers, IBM divided the system BIOS into real mode and protected mode parts. The real-mode portion was intended to provide backwards compatibility with existing operating systems such as DOS, and was therefore called "CBIOS" (for "Compatibility BIOS"), while "ABIOS" (for "Advanced BIOS") provided new interfaces specifically suited to multitasking - Operating systems such as OS/2.
The original IBM PC and XT BIOS did not have an interactive user interface. Error codes or messages were displayed on the screen, or a series of coded beeps were generated to indicate errors when the power-on self-test (POST) did not progress to the point where a video display adapter successfully initialized.
Options on the IBM PC and XT were set by switches and jumpers on the motherboard and on expansion cards. Beginning in the mid-1990s, it became typical for BIOS ROMs to include a "BIOS Setup Utility" (BCU) or "BIOS Setup Utility" that is accessed at power-on using a specific key sequence. This program allowed the user to set system configuration options of the type previously set via DIP switches through an interactive keyboard driven menu system.
