Both the M systems Flash card in a ISA slot and the Disk-On-A-Chip require that the C be set to none. Both of these devices require special software when setting them up.
Example: The special floppy for the flash card cannot be locked. The machine boots from it, loads software, writes to the floppy autoexec so the next boot it goes to step 2. So now it automatically reboots, executes step two (loading minimum DOS), does this all over again, and executes step 3. In this final step it writes to the floppy autoexec again and sets it back to step 1. Then machine software is loaded.
If a virus is contracted on one of these devices, it is toast.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)