Non-GUI Client: These are applications, generate server requests with a minimal amount of human interaction.

GUI Clients: These are applications, where occasional requests to the server result from a human interacting with a GUI

(Example: Windows 3.x, NT 3.5)

OOUI clients : These are applications, which are highly-iconic, object-oriented user interface that provides seamless access to information in very visual formats.

(Example: MAC OS, Windows 95, NT 4.0)