FDOS may refer to:
Floppy Disk Operating System, a term sometimes used to describe early floppy-based disk operating systems such as CP/M FDOS, an operating system developed by iCOM Microperipherals (later iCOM-Pertec) in 1975, and available as an option bundled with iCOM's floppy drives available for the Intellec series of computers by Intel and the MITS Altair, FDOS, the part of the Basic Disk Operating System (BDOS) implementing the filesystem in Digital Research operating systems such as the CP/M and DR-DOS families FreeDOS, a free disk operating system FDOS, First Day of Service
See also DOS (disambiguation) FOS (disambiguation)