8/6/2019 12705_about BIOS (2)

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ROM with BIOS

Prior to the early 1990s, 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. PROM chips may be erased by prolonged exposure to ultraviolet light,

which accessed the chip via the window. Chip manufacturers use PROM blasters to

reprogram EPROM chips. 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 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.

EEPROM chips are advantageous because they can be easily updated by the user; hardware

manufacturers frequently issue BIOS updates to upgrade their products, improve

compatibility and remove bugs. However, this advantage had the risk that an improperly

executed or aborted BIOS update could render the computer or device unusable.

Virus attacks

There was at least one virus named CIH (also known as "Chernobyl Virus") which was able

to erase Flash ROM BIOS content, rendering computer systems unusable. Affected systems

often can't be fixed on their own since they're no longer able to boot. In such scenario Flash

ROM IC should be ejected from motherboard and reprogrammed somewhere else. All

modern operating systems like Windows XP, Windows Vista, Linux  just do not allow direct

hardware access to usual non-privileged programs. So, as of year 2008 CIH became almost

harmless and at very most just bothers users by infecting executable files without being able

to cause any real harm and only toggling numerous virus alerts from antivirus software.

Major BIOS vendors include American Megatrends (AMI), Insyde Software, Phoenix

Technologies (which bought Award Software International in 1998 and General Software in

2008) and Byosoft (which is a Chinese firmware company located at Nanjing, China).

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