These are the utilities I've written for working with my Cromemco Z2-D, a S-100 system using the Cromemco ZPU and 4FDC.
Bare metal disk loader for the Cromemco 4FDC and RDOS 1.x. Requires formatted SSSD 5.25" floppies. Images are "typed" into RDOS one track at a time, and saved to disk using RDOS's disk commands. Quite slow, but functional! Usage:
./diskloader.pl image.bin /dev/ttyS0
Where image.bin is a raw Cromemco binary disk image, and /dev/ttyS0 is a serial port connected to the 4FDC's console. Before running diskloader.pl, connect to the console port and autobaud.