Is the destination drive drive/head register when the drive bit in the register is changed? So will switching from drive 0 to 1 or vise versa update the other bits in said register? Or will they stay unchanged?
Edit: Just now made it match Bochs behaviouir: writing either master or slave drive/head register writes both master and slave(with the only difference being the high 2 bits(bits 7&5) forced set and the DRV bit being set to 0 or 1 depending on the drive affected(master=0 slave=1).
Previously it would just write whatever value was written only to the master or slave that's selected on bit 4(updating the drive selected before writing said register).

Would this change actually affect any software, OS or BIOS?