Real mode BIOS routine and Protected Mode

I am doing some OS experiment. Until now, all my code utilized the real mode BIOS interrupt to manipulate hard disk and floppy. But once my code enabled the Protect Mode of the CPU, all the real mode BIOS interrupt service routine won't be available. How could I R/W the hard disk and floppy? Do I need to do some hardware drivers now? How could I start? Is this one of the reasons that an OS is so difficult to develop?

I know that hardwares are all controlled by reading from and writing to certain control or data registers. For example, I know that the Command Block Registers of hard disk range from 0x1F0 to 0x1F7. But I am wondering whether the register addresses of so many different hardwares are the same on the PC platform? Or do I have to detect that before using them? How to detect them??

Since I am not sure about how to R/W floppy or hard disk in Protect Mode, I have to use the BIOS interrupt to load all my necessary kernel file from floppy into memory for now. But what could I do if my kernel file exceeds the real mode 1M space limit?

For any responses I present my deep appreciation.

Update

I vaguely recall that there's a way to switch Protected Mode first and then switched back to real mode. And then we could use the BIOS routine in Protected Mode. Maybe I remember wrong. Did someone remember it right?