A directory system can be classified in to single level and hierarchical directory system:
Single level directory system: In this type of directory system, there is a root directory which has all files. It has a simple architecture and there are no sub directories. Advantage of single level directory system is that it is easy to find a file in the directory. This type of directory system is used in cameras and phones.
Hierarchical directory system: In a hierarchical directory system, files are grouped together to form a sub directory At the top of the hierarchy is the root directory and then there are sub directories which has files. Advantage of hierarchical directory system is that users can be provided access to a sub directory rather than the entire directory. It provides a better structure to file system. Also, managing millions of files is easy with this architecture. Personal computers use hierarchical directory system for managing files.