I am trying to get a better understanding of how BIOS and operating systems work. From what I understand, BIOS is a basic piece of software that is the first thing to be run when a computer turns on and loads the operating system. I also understand that the BIOS is written by the company that makes the computer. For example, Dell writes the BIOS for Dell computers. Please correct me if any of this is wrong.
I have been told that computers that get Windows 8 OS installed can no longer access the BIOS when the computer turns on. How does this work? It seems that the only way this would work is if the BIOS was dependent on the OS, but that doesn't really make sense.
Best Answer
When an x86 computer is first turned on, it is operating in what is known as "real mode". The hardware starts running the BIOS, which loads the operating system, and transfers control to it.
Shortly after this, the operating system turns on what is known as "protected mode". In protected mode, there are basically two kinds of code: kernel code (like the operating system and drivers), and user code (like everything else).
In order to use the features of the BIOS, it is necessary to operate in kernel mode. Once Windows starts, only Windows is able to run in kernel mode (Windows, and anything else that Windows decides can also run in kernel mode).
Normal (user mode) code cannot call on the BIOS once the operating system has started. Only the operating system and drivers and other such kernel mode software can access the BIOS.