2. BIOS

There is a small program called the BIOS (Basic Input Output System) that is responsible for booting up the computer. It is not part of the operating system as it has to work before the operating system is even loaded.

It is normally stored on a BIOS chip on the motherboard. This chip contains non-volatile memory: either ROM in older systems, or Flash memory in newer ones.

The BIOS contains the most basic hardware settings of the computer and a set of instructions to begin the boot up process.

This is a typical BIOS setup screen

Within the BIOS, there are settings for the hardware. Such as hard disk details, memory capacity, memory timing information, optical drive details.

The boot order can also be set that tells the BIOS which drive to look to, for the operating system. For example it could be told to first look in the optical drive, then an USB port then the primary hard disk.