Overview
Historically, and even on some modern embedded devices, the file systems either have no support for directories at all or only have a "flat" directory structure, meaning subdirectories are not supported; there is only a group of top-level directories each containing files. The first popular fully general hierarchical file system was that of Multics. This type of file system was an early research interest of Dennis Ritchie.
Most modern Unix-like systems, especially Linux, have a standard directory structure defined by the Filesystem Hierarchy Standard.
In many operating systems, programs have an associated working directory in which they execute. Typically, file names accessed by the program are assumed to reside within this directory if the file names are not specified with an explicit directory name.
Some operating systems restrict a user's access to only their home directory or project directory, thus isolating their activities from all other users.
Unix systems treat directories as a type of file.
Read more about this topic: Folder (computing)