Topics: BIOS, Booting, Operating system Pages: 13 (4572 words) Published: November 27, 2013
This article is about the BIOS as found in IBM PC compatibles. For the general concept, see Firmware. For other uses, see Bios. In IBM PC compatible computers, the Basic Input/Output System (BIOS), also known as System BIOS, ROM BIOS or PC BIOS (/ˈbaɪ.oʊs/), is a de facto standard defining a firmwareinterface.[1] The name originated from the Basic Input/Output System used in the CP/M operating system in 1975.[2][3] The BIOS software is built into the PC, and is the first software run by a PC when powered on. The fundamental purposes of the BIOS are to initialize and test the system hardware components, and to load a bootloader or an operating system from a mass memory device. The BIOS additionally provides abstraction layer for the hardware, i.e. a consistent way for application programs and operating systems to interact with the keyboard, display, and other input/output devices. Variations in the system hardware are hidden by the BIOS from programs that use BIOS services instead of directly accessing the hardware. Modern operating systems ignore the abstraction layer provided by the BIOS and access the hardware components directly. The BIOS of the original IBM PC/XT had no interactive user interface. Error messages were displayed on the screen, or coded series of sounds were generated to signal errors. Options on the PC and XT were set by switches and jumpers on the main board and on peripheral cards. Modern Wintel-compatible computers provide a setup routine, accessed at system power-up by a particular key sequence. The user can configure hardware options using the keyboard and video display. BIOS software is stored on a non-volatile ROM chip on the motherboard. It is specifically designed to work with each particular model of computer, interfacing with various devices that make up the complementary chipset of the system. In modern computer systems, the BIOS contents are stored on a flash memory chip so that the contents can be rewritten without removing the chip from the motherboard. This allows BIOS software to be easily upgraded to add new features or fix bugs, but can make the computer vulnerable to BIOS rootkits. MS-DOS (PC DOS), which was the dominant PC operating system from the early 1980s until the mid 1990s, relied on BIOS services for disk, keyboard, and text display functions. MS Windows NT, Linux, and other protected mode operating systems in general do not use it after loading. BIOS technology is in a transitional process towards UEFI since 2010[4] Contents

1 Terminology
2 The BIOS boot process
2.1 Boot devices
2.2 BIOS extensions
2.3 Boot environment
3 Operating system services
4 BIOS components
5 User interface
6 Chips
7 Flashing the BIOS
8 Overclocking
9 BIOS chip vulnerabilities
9.1 Virus attacks
10 BIOS Boot Specification
11 Changing role of the BIOS
11.1 SLIC
11.2 Reprogrammable microcode
12 The BIOS business
13 Comparison
14 See also
15 References
16 Further reading
17 External links
17.1 Specifications
The term BIOS (Basic Input/Output System) was invented by Gary Kildall[5] and first appeared in the CP/M operating system in 1975,[2][3][6][7] describing the machine-specific part of CP/M loaded during boot time that interfaces directly with the hardware.[3] (A CP/M machine usually has only a simple boot loader in its ROM.) Versions of MS-DOS or PC DOS contain a file called variously "IO.SYS", "IBMBIO.COM", "IBMBIO.SYS", or "DRBIOS.SYS"; this file is known as the "DOS BIOS" (aka "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 the analogous to the "CP/M BIOS". In other types of computers, the terms boot monitor, boot loader, and boot ROM are used instead. Some Sun and PowerPC-based computers use Open Firmware for this purpose. With the introduction of PS/2 machines, IBM...
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