Information output system

A display unit having a communication control circuit for communicating with an externally connected computer, wherein said communication control circuit including comparing means for comparing a first identification information which is previously stored in the display unit, and a second identification information which is previously stored in the computer and is sent from the computer. A communication permission means for enabling display control by the computer and permitting communication between said computer and the display unit with respect to display control of the display unit, when the first and second identification information match as a result of the comparison by the comparing means.