The Input-Process-Output (IPO) Model, also known as the IPO+S Model, is a functional model and conceptual schema of a general system.
The components of the IPO model are defined as:

• I: Input – The information, ideas, and resources used in creating a program
• P: Processing – Actions taken upon/using input or stored material
• O: Output – Results of the processing that then exit the system
• S: Storage – Location(s) where material inside the system is/are placed for possible use at a later point in time