The Unix Filesystem 12.3. The Virtual Filesystem One of the unique things about Unix as an operating system is that regards everything as a file. Device files include things such as disks, cdroms, tapes, terminals, serial ports, and sound cards.
All files contain data of some kind.
Ordinary or plain files are most likely to contain data that are meaningful to users. Plain files may contain data that users have entered into the computer, data that have been generated by programs, and even programs themselves. Indeed, all programs exist as files, and nearly all Unix commands result in a program file being retrieved and executed. This is an important feature and contributes to the flexibility of Unix. Unix directory structure Directories in Unix are properly known as directory files.