[LinuxBIOS] Question about protect mode?

[Fu xiayin]

Hello,everyone.
I'm a student, and now my  task is studying Linuxbios.

I'm not very clear about the difference between the protect mode and the
real mode.
So I wonder why should Linuxbios turn into protect mode at the very
beginning.

And is there any difference between protect mode in  Linuxbios and in linux
kernel.
If any, what's the main difference?