It is possible to separate the use of computers for instructional purposes into four modes, distinguished by the style of user interaction and sometimes by the implementation methods used. The four major modes are: 1) conversational, in which the interaction resembles an exchange between two persons; 2) data-based, wherein one component of the man-machine system extracts from the other information useful to the solution of a problem; 3) computational, in which the user focuses upon the computational power of the computer; and 4) drill, a repetitive, structurally fixed interaction in which only the specific contents are changed. Classifications of this sort overemphasize difference between styles of use, but attending to structural and pedagogical attributes has its uses. It provides a framework for characterizing system capabilities and applications, a shorthand for communication among computer scientists, and guidelines for novice authors of instructional material. (PB)