There was a time when some disks were manufactured with an interface for only type of hardware, which might only have one OS with drivers available, but an interface and drivers could be created for any disk drive if there was a need.
Drives can be physically partitioned to maintain multiple OSs. Some OS can be run within the file system of another. And there are also emulators that can provide different OS functionality, and Virtual Machines that can run multiple OS. Those are variations of running an OS within the file system of another OS.