<P> The original IBM PC BIOS (and cassette BASIC) was stored on mask - programmed read - only memory (ROM) chips in sockets on the motherboard . ROMs could be replaced, but not altered, by users . To allow for updates, many compatible computers used re-programmable memory devices such as EPROM and later 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 ultraviolet erasable PROM (EPROM) chips . Flash chips are programmed (and re-programmed) in - circuit, while EPROM chips need to be removed from the motherboard for re-programming . BIOS versions are upgraded to take advantage of newer versions of hardware and to correct bugs in previous revisions of BIOSes . </P> <P> 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 . </P> <P> 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). In 2006, the first systems supporting a Serial Peripheral Interface (SPI) appeared, and the BIOS flash memory moved again . </P> <P> The size of the BIOS, and the capacity of the ROM, EEPROM, or 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 16 megabytes . For contrast, the original IBM PC BIOS was contained in an 8 KiB mask ROM . Some modern motherboards are including even bigger NAND flash memory ICs on board which are capable of storing whole compact operating systems, such as some Linux distributions . For example, some ASUS motherboards included Splashtop Linux embedded into their NAND flash memory ICs . However, the idea of including an operating system along with BIOS in the ROM of a PC is not new; in the 1980s, Microsoft offered a ROM option for MS - DOS, and it was included in the ROMs of some PC clones such as the Tandy 1000 HX . </P>

Where is the bios stored in a computer