BIOS, which stands for Basic Input and Output system is the piece of software which resides in a chip on the motherboard. Without BIOS a system cannot start and this is the software which identifies, controls, and maintains a log of all the hardware devices (directly connected to the motherboard) and their settings on your computer. It is the duty of BIOS to check all the connected devices like Hard Drives processor, memory, video card etc for there presence and proper functioning at the time of startup. This is executed in the very beginning of system startup and this passes the control to the operating system after loading the core files of it. There are many settings saved in the BIOS which we might need to change whenever required. You would have noticed the line which asks us to press F1 (or any other Key) to enter system. This is how we enter into BIOS.
Entering into BIOS does not depend upon what operating system you have because BIOS comes way before the operating systems gets loaded into the memory. Even if we do not have any operating system installed on our computer still we can enter in the BIOS and make the changes or know about various settings present in it. On entering the BIOS we get a graphical interface which can only be operated through the keyboard. BIOS does not support mouse enabled interface because Mouse is not a necessary device and your computer will boot and work fine even if you do not have a mouse connected, but yes in that case you should be good with the keyboard shortcuts. Once we are inside any BIOS we can use the Mouse keys to scroll or move through various sections of BIOS and the same can be used for entering the new values. BIOS navigation help is always available on the every page of the BIOS which keeps on telling us which key to use to do what. There are three main BIOS manufacturers which makes a computer system BIOS. These three are AMI (American Megatrends, Inc), Award, and Phoenix. The computer manufacturers or the motherboard manufacturing companies use the BIOS made by any of these three to power there computers.
Depending upon the computer and the BIOS you have on your computer the key to enter in it varies. Given below are the key combinations used in some most popular computer systems for opening the BIOS installed in it.