No multi-tasking doesn't mean it can't be an OS, just not a decent OS. DOS was not a multi-tasking OS. Prior to ITS, the MIT AI Lab (which RMS was a member of)

No multi-tasking doesn't mean it can't be an OS, just not a decent OS. DOS was not a multi-tasking OS. Prior to ITS, the MIT AI Lab (which RMS was a member of) were opposed to multi-tasking OSs. Lack of that feature doesn't make it not an OS.