The word hierarchy comes from the Greek hieros, meaning sacred, and archein, meaning to rule. The word first entered English in the fourteenth century. According to the Oxford English Dictionary, it originally referred to “Each of the three divisions of angels, every one comprising three orders, in the system of Dionysius the Areopagite.”
A hierarchy is an organizational structure in which items are ranked according to levels of importance. Most of the governments, corporation and organized religions are hierarchical.
In a computing context there are various types of hierarchical systems. Most of the file systems are based on a hierarchical model in which files are placed somewhere in a hierarchical tree model. A file is placed in a directory or subdirectory at the desired place in the structure. The computer memory hierarchy ranks the components in terms of response times with processor register at the top of the pyramid structure.
Fig: Hierarchy of Operating System.
