Functionality of a computer

A computer is a complex system,contemporary computers contain millions of elementary electronic components.Then how can we clearly describe how these work and function,hence we find the hierarchy of the system on order to resolve the functionality of each and every unit of the system,the same works with the computer too.
Hence we figure out a hierarchical format for the computer.
A hierarchical system if a set of interrelated subsystems, each of the latter, in turn, hierarchical in structure until we reach some lowest level of elementary subsystem.
The hierarchical nature of complex systems is essential to both their design and their description.The designer need only deal with a particular level of the system at a time.At each level,the system consists of a set of components and their interrelationships.The behavior at each level depends only on a simplified, abstract characterization of the system at the next lower level.
At each level, the designer is concerned with structure and function:
Structure:The way in which the components are interrelated.
Function: The operation of each individual components as part of the structure.

Basically to design a computer, we begin with the major components of a computer, describing their structure and functionality, and proceed to successively lower layers of the hierarchy.

Function:
Both the structure and the functionality of a computer are in essence and can be depicted by the following features that they perform that is the functionality of a computer or the functions that the computer can perform.They are:

• Data processing
• Data storage
• Data movement
• Control

The TOP-LEVEL structure of a computer: