a way of organizing and storing files on a disk or other storage device (= a device for storing computer information). Different file systems are used by different operating systems (= sets of programs that control the way a computer system works)

Restore the backup of the file system into the new file system.

A directory is simply a file that has special meaning to the filesystem. 对文件系统来说，目录只是一个有特殊意义的文件。