BIOS

BIOS

The BIOS is boot firmware, designed to be the first code run by a PC when powered on. The initial function of the BIOS is to identify, test, and initialize system devices such as the video display card, hard disk, floppy disk and other hardware. The BIOS sets the machine hardware into a known state, so that software stored on compatible media can be loaded, executed, and given control of the PC.This process is known as booting, or booting up, which is short for bootstrapping.
One of the most common uses of Flash memory is for the basic input/output system of your computer, commonly known as the BIOS. On virtually every computer available, the BIOS makes sure all the other chips, hard drives, ports and CPU function together.

Every desktop and laptop computer in common use today contains a microprocessor as its central processing unit. The microprocessor is the hardware component. To get its work done, the microprocessor executes a set of instructions known as software .When BIOS boots up (starts up) your computer, it first determines whether all of the attachments are in place and operational and then it loads the operating system (or key parts of it) into your computer's random access memory ( RAM  ) from your hard disk or diskette drive.

With BIOS, your operating system and its applications are freed from having to understand exact details (such as hardware addresses) about the attached input/output devices. When device details change, only the BIOS program needs to be changed. Sometimes this change can be made during your system setup. In any case, neither your operating system or any applications you use need to be changed.

* The operating system - The operating system provides a set of services for the applications running on your computer, and it also provides the fundamental user interface for your computer. Windows 98 and Linux are examples of operating systems.
* The applications - Applications are pieces of software that are programmed to perform specific tasks. On your computer right now you probably have a browser application, a word processing application, an e-mail application and so on. You can also buy new applications and install them.

BIOS programs are stored on a chip and are built to work with various devices that make up the complementary chipset of the system. They provide a small library of basic input/output functions that can be called to operate and control the peripherals such as the keyboard, text display functions and so forth. In the IBM PC and AT, certain peripheral cards such as hard-drive controllers and video display adapters carried their own BIOS extension ROM, which provided additional functionality. Operating systems and executive software, designed to supersede this basic firmware functionality, will provide replacement software interfaces to applications.
BIOSes were stored in ROM or PROM chips, which could not be altered by users. As its complexity and need for updates grew, and re-programmable parts became more available, BIOS firmware was most commonly stored on EEPROM or flash memory devices. According to Robert Braver, the president of the BIOS manufacturer Micro Firmware, Flash BIOS chips became common around 1995 because the electrically erasable PROM (EEPROM) chips are cheaper and easier to program than standard erasable PROM (EPROM) chips. EPROM chips may be erased by prolonged exposure to ultraviolet light, which accessed the chip via the window. Chip manufacturers use EPROM programmers (blasters) to program EPROM chips. Electrically erasable (EEPROM) chips come with the additional feature of allowing a BIOS reprogramming via higher-than-normal amounts of voltage.BIOS versions are upgraded to take advantage of newer versions of hardware and to correct bugs in previous revisions of BIOSes.

The first flash chips were attached to the ISA bus. Starting in 1997, the BIOS flash moved to the LPC bus, a functional replacement for ISA, following a new standard implementation known as "firmware hub" (FWH). Beginning with the IBM AT, PCs supported a hardware clock settable through BIOS. It had a century bit which allowed for manually changing the century when the year 2000 happened. Most BIOS revisions created in 1995 and nearly all BIOS revisions in 1997 supported the year 2000 by setting the century bit automatically when the clock rolled past midnight, December 31, 1999.In 2006, the first systems supporting a Serial Peripheral Interface (SPI) appeared, and the BIOS flash moved again.

The size of the BIOS, and the capacities of the ROM, EEPROM and other media it may be stored on, has increased over time as new features have been added to the code; BIOS versions now exist with sizes up to 8 megabytes. Some modern motherboards are including even bigger NAND Flash ROM ICs on board which are capable of storing whole compact operating system distribution like some Linux distributions. For example, some recent ASUS motherboards included SplashTop Linux embedded into their NAND Flash ROM ICs.

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