What is BIOS ?

 Stand for basic input/output system, also the built-in software that determines what a computer can do without accessing programs from a disk.

•  The BIOS is usually placed in a ROM chip that comes with the computer (it is often called a ROM BIOS). This ensures that the BIOS will always be available and won't be damaged by disk failures. It also makes it feasible for a computer to boot itself. Because RAM is faster than ROM, though, plenty of computer manufacturers design systems so that the BIOS is copied from ROM to RAM each time the computer is booted. This is known as shadowing. .
• The PC BIOS is standardized, so all PCs are similar at this level (although there's different BIOS versions). Additional DOS functions are usually added through software modules. This means you can upgrade to a newer version of DOS without changing the BIOS.
• Plenty of modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary
• On PCs, the BIOS contains all the code required to control the keyboard,display screen, disk drives, serial communications, and a few miscellaneous functions, and it can handle Plug-and-Play (PnP) devices are known as PnP BIOSes, or PnP-aware BIOSes. These BIOSes are always implemented with flash memory than ROM.