High-level features of the UNIX system such as the file system, the processing environment, and building block primitives (for example, pipes).
The File System:-
The UNIX file system is characterized by
- a hierarchical structure, consistent treatment of file data,
- the ability to create and delete files,
- dynamic growth of files,
- the protection of file data,
- the treatment of peripheral devices (such as terminals and tape units) as files.
Programs in the UNIX system have no knowledge of the internal format in which the kernel stores file data, treating the data as an unformatted stream of bytes. Programs may interpret the byte stream as they wish, but the interpretation has no bearing on how the operating system stores the data.
Directories are like regular files in this respect; the system treats the data in a directory as a byte stream, but the data contains the names of the files in the directory in a predictable format so that the operating system and programs such as Is (list the names and attributes of files) can discover the files in a directory.
Permission to access a file is controlled by access permissions associated with the file. To the user, the UNIX system treats devices as if they were files.