What information does BIOS load into RAM?

Question

I know that, on booting, BIOS loads the first sector (512 bytes) of a pre-defined device drive on memory 0x7c00 and then jump to that address.

So, memory from 0x7c00 to

Answer 1

If you write an OS, as soon as you go into protected mode, you get forget the BIOS (unless you are working with some bad device) and use all you have.

Or are you writing a bootloader?