In order to see how the "file system" works, you can create your own Unit tests or just run and analyze the existing ones. There is also a graphical representation of the system implemented using Swing.
Baksonator/fat16
A simulation of the FAT16 file system written in Java. I worked on it as part of an assignment for a course on university. Most of the underlying classes are not my work, my assignment was to work on the classes MockFAT and MockDirectory classes. I additionally added the DiskFile class.
Java