Every storage device has a principal directory, known as the root directory. All other files and directories are stored within the root directory. Directories can be nested, meaning it is possible to store sub-directories, as well as files, within a directory. Nesting can take place to any depth.
A PC might have three folders in the root directory, one holding letters, a second the manuscript of a book and the third storing program. A few miscellaneous documents are also stored within the root directory, as shown in the following diagram:
Each file and folder must have a name which is unique at that level. It is not possible to have two files with the same name in the same folder, but we could have two files with the same name in different folders.
On most multi-user systems, the system administrator will allocate each user their own directory (often called by their username) and can arrange their own files and folders within that as they choose.
A user cannot normally see any other user's files, unless the other user explicitly permits them to do so by sharing the files. Users can also set permissions for other users or groups of users, specifying whether they are allowed to read, write or modify files.
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