What are the three categories of computers?

The Supercomputer, the server, and the workstation.

Supercomputers are dedicated processing clusters that manipulate data until it reaches a wanted result or calculates all possible results. A percentage of calculation time can be allotted to certain group at the discretion of the organization.

Servers are computers that provide services to other computers. This may be relaying e-mail messages, verifying credentials, or retrieving data such as web pages. Typically users do not physically interact with a server.

Workstations, terminals, and PCs are computers that users usually sit in front of. They are the smallest and most numerous of the three. Installed applications provide productivity, data access, and or recreation to the user.