High Quality Content by WIKIPEDIA articles! The Cromemco 4FDC Floppy Disk Controller is designed to interface both 5- and 8-inch floppy disk drives to the S-100 computer bus used in Cromemco and other IEEE 696 computers. It also contains an RS232 serial I/O channel with software-selectable baud rates from 110 to 76,800. In addition, it has a 1K resident 2708 ROM containing Cromemco`s RDOS, the Resident Disk Operating System.