- The x86 BIOS: Its Limits and Capabilities
- 16- and 32-Bit Code
- The BIOS as Driver for DOS
- Modern Uses of the BIOS
- What BIOS Do You Have?
- Add-On Card BIOSs
- Video BIOSs
- Boot BIOSs for SCSI and Networking
- Additional BIOSs
- BIOS Updates
- EIDE and SCSI Hard Disk Handling
- Understanding CHS Geometry Limits
- Getting Around the 1024-Cylinder Limit
- Common BIOS Disk Utilities
- The Handoff to the OS
All modern PCs include flash BIOSs. These are BIOSs that can be overwritten by the user. They reside on electrically erasable programmable ROMs (EEPROMs), which can be reprogrammed while residing in the motherboard. This can be a great feature because you can upgrade your BIOS to eliminate bugs or add features. Typically, the BIOS update utilities are DOS programs, so you need a DOS partition or a DOS boot floppy (the latter is generally safer).
BIOS updates are extremely useful but also potentially quite dangerous. If you select the wrong BIOS file or if something goes wrong during the flash process, your computer will be rendered unbootable. The only way to correct this problem is to replace the BIOS chip in the motherboard. As a safety precaution, I recommend keeping a backup of your existing BIOS file on a floppy disk (most flash utilities provide an option to create such a backup). That way, if your upgrade goes badly, you can take your computer and the floppy to a local computer dealer to have a fresh BIOS chip flashed and installed. Better yet, if you can obtain a spare preprogrammed BIOS chip, you'll have it on hand if anything goes wrong. Some motherboards include an unflashable BIOS in addition to the flash BIOS, so you can recover from such a disaster more easily.
You can check your motherboard manufacturer's Web site for information on updating your BIOS. Similar updates are often available for video cards, SCSI host adapters, and other devices that contain BIOSs. Because of the dangers involved in updating a BIOS, I recommend doing so only if you're having problems that you believe might be solved by a BIOS update. Many BIOS updates are issued only to fix problems experienced by a few people or to add features that you might not need. There's no sense in risking making your system unusable for an "improvement" that won't help you.
Be sure to use a BIOS update file only for the motherboard make and model that you're using. Some manufacturers release motherboards that are very different but that have model numbers that differ by only one character. Using the wrong BIOS file can produce an unbootable system. If you're a more advanced user, you might think that using a BIOS file for a board that uses the same chipset as yours will work. This might indeed be true, but it might also produce an unbootable system because of different customizations used by each manufacturer.