Floppy disk controller
The floppy disk controller is used to control up to 4 floppy disk drives.
In the PC computer, it was originally based on a Nec uPD765 chip. On the PC/AT, a register was added to inform the OS that the media changed, and several other registers were added in the PS/2 and Model30 computers. Enhanced controllers were then implemented, with new functions and support of perpendicular mode, generally based on the Intel 82077AA chip.