The BIOS is Basic Input/Output System used by a computer which embedded on a chip on a computer's motherboard. It is used to controls various devices connected to your computer. When you turns on the computer, the BIOS starts up and performs a Power-On Self Test (POST). The BIOS will check all devices connected to your computer such as the CPU, RAM, the video card, the sound card and so on. Once the post test has completed, the BIOS will looks for Linux operating systems on the hard drive. At this point, the Linux takes over control of your computer and finishes starting up system in GUI or text based mode.
Today the BIOS is stored in rewritable memory which allows you to update old BIOS firmware with a newer version. This is known as flashing. This is done by a special program provided by the computer manufacturer. A newer version fix bugs, may provide improved performance and/or may support newer hardware devices such as large hard drives or SCSI / SAS disks etc. You do not need to use MS-Windows or MS-DOS system for flashing the BIOS. You can use the Linux operating system. Here are some good articles that explain the BIOS flashing using Linux:
=> BIOS Upgrade documentation from thinkwiki.
=> Another good how-to located at Gentoo forum.
=> biosdisk simplifies the process of flashing your system BIOS under Linux on Dell desktops and laptop. For Dell servers use different rpm provided by Dell.
=> You can use FreeBIOS project for flashing using native Linux tools i.e. no .exe files (a quick howto is here)