Some user interfaces, such as that of Unix(1) are difficult fur novices to
use, and this paper suggests a possible solution to such problems. The resu
lts of a study of Unix users enabled the development of a taxonomy of error
types so that users' errors can be classified. This information is encapsu
lated as production rules within a knowledge base and forms the basis for t
he design and development of an intelligent interface to Unix. The prototyp
e makes inferences about users' mental models and uses these to select appr
opriate tutorial advice. Performance of users of the prototype intelligent
interface was compared with that of users of the usual Unix interface. The
prototype users were found to make fewer errors, exhibit fewer misconceptio
ns and take less time to complete a standard set of tasks.