File System and how data is stored.
Any file system in OS basically tells what is the positioning of data on mounted storage. In the absence of a file system the OS cannot know while files are present, starts where and ends where ?
The type of file system defines the way data is stored or kept inside a storage area.
It depends on the OS to which file system needs to be used and its totally OS dependent. In the case of an unsupported file system the behaviour is the same as the data stored with no file system.