The modern approach in teaching computer architecture is to describe the computing machine in terms of its major units (store, processor, etc.) and then to describe each of these units in progressively greater detail. This contrasts with the earlier approach in which individual gating circuits were described, and later developed into larger units. The older approach lends itself well to laboratory work in which a few components or circuits may be assembled and tested in a short time. The cost of this is small, and a whole class of students may perform a useful exercise with relatively small overhead. In contrast, the modern approach requires the student to design and/or modify a complete computer structure from relatively large units. Providing sufficient equipment to support this approach is too expensive to contemplate.