The BIOS is the Basic Input / Output System. It is a special chip that contains a basic operating system that enables the computer to start up and function. When you turn on your computer the BIOS determines what hardware is installed on the computer.  It then runs the POST (Power On Self Test), which is part BIOS. The POST ensures that all of the critical system components are starting and functioning correctly. It indicates when a critical component is found to not be working. The BIOS then does a search for a hard drive and looks for its boot block. The boot block is the part of the drive set up to point to the files that start the operating system.

BIOS are stored on the ROM (Read Only Memory) part of the EPROM (Erasable / Programmable Read Only Memory). The ROM is preset with what it can do and the hardware it can work with. Sometimes, the BIOS must be upgraded if new, unsupported hardware is added to the computer. Newer BIOS chips use Flash memory which allow the BIOS to be easily updated. There is a battery attached to the motherboard to maintain power to the memory in which the hardware configuration is stored. The BIOS on newer computers have a setup utility so that you can edit the hardware configuration.

The job of the BIOS, after it starts up the operating system, is to provide a link into the system's critical components [such as the RAM, CPU, I/O controller, and the video card]. In most cases the BIOS' contents are shadowed in (copied to) RAM, so that it can be read faster.

PLUG AND PLAY BIOS interacts with compatible hardware and the operating system, allowing the computer to automatically detect and configure hardware that is installed.