A computer is a device (usually electronic) that is capable of storing and retrieving data and of executing logical or mathematical operations without human intervention.
 
 
 

Or in other words: A computer is a fast, accurate moron, while a human being is a slow, error-prone genius.
 
 
 

It (the computer) can do whatever we know how to order it to perform. Its province is to assist us in making available what we are already acquainted with. -Augusta Ada Byron
 

• A telephone is a technology that externalizes our ability to communicate.
• A cup is a technology that externalizes our ability to hold things (liquid).
• A piano is a technology that externalizes our ability to make (pleasant) sounds.