BIOS is a very important program indeed. Its quality and how modern it is determine the features and capabilities of your machine to a large degree. The most striking example of this is support for IDE/ATA hard disks over 504 MB; the only change necessary to support these larger drives in most cases is a BIOS capable of doing the geometry translation. There are other examples as well; many motherboard manufacturers are able to expand the capabilities of their boards, or fix problems with them, by making changes to the BIOS and either giving free downloads or selling upgrades, just as software application houses like Microsoft, Lotus, etc. do.

The BIOS program in your PC is programmed into a read-only memory (ROM). ROMs are, of course, not rewriteable the way RAM is; that is why they are called "read-only". This presents a problem when you want to update your BIOS. In "the old days" when you wanted to update your BIOS, the manufacturer sent you a new BIOS chip; you opened the box, pulled out the old chip, and put the new one in. Needless to say, this is a pain. Fortunately, technology came to the rescue through the invention of the flash BIOS. Some machines still require the physical upgrade but by using the flash BIOS, most newer machines can upgrade using special software without having to open the case at all.

Machines with flash BIOS capability use a special type of BIOS ROM called an EEPROM; this stands for "Electrically Erasable Programmable Read-Only Memory". As you can probably tell by the name, this is a ROM that can be erased and re-written using a special program. This procedure is called flashing the BIOS and a BIOS that can do this is called a flash BIOS. The advantages of this capability are obvious; no need to open the case to pull the chip, and much lower cost.

Many motherboards have a special "safety feature" to prevent accidental (or malicious) changes to the flash BIOS--a jumper that must be changed before performing a flash BIOS upgrade. While this is a security feature, it also obviates one of the great advantages of the flash BIOS, namely not having to open the case! Your motherboard manual will tell you whether you have a jumper or not. With the increasing commonality of viruses that can change flash BIOS code, this may soon be a feature on every motherboard.

There is one big disadvantage to using the flash process to upgrade your BIOS. While the BIOS is actually being flashed, it is in a very vulnerable state. If you are really unlucky and something very bad happens in the middle of the upgrade (for example, a power outage), it is possible to end up with a corrupted BIOS chip. You can also end up with a corrupted system if you boot the wrong flash BIOS image into the chip--motherboard manufacturers usually use an unintelligent, universal flash program that will happily program the entirely wrong BIOS image into your system if you tell it to! Fortunately, some manufacturers are now making these programs smarter. For example, Award's flash program checks the name of the image file against the model of motherboard and will complain if there is a mismatch.
In addition, the motherboard may support the boot block process. This process can be used for BIOS recovery.

If your system becomes corrupted to the point where it will not boot, you are in a catch-22. Your BIOS is corrupted, so you can't boot the PC, and since you can't boot the PC there's no conventional way to re-flash the BIOS. See this section in the troubleshooter for ideas on recovering from this problem.

Fortunately, BIOS chip corruption is quite rare; the BIOS is a small program and flashing it usually takes only a few seconds. Still, it's not something to try in the middle of a thunderstorm, and I try to use a UPS when doing this type of work, if possible. And be sure you are using the right BIOS image.