This paper explores the concept of using minimal configuration microcomputer systems for use with computer-aided design optimization software. Two different approaches - EPROMs and audio cassettes - were examined. The advantages were ease of use, portability and low costs. It is believed that small, portable, custom-built “design boxes” of this type have a role both in design offices and as on-board machine controllers. Indeed they may be the beginning of an integration of these roles, in a limited kind of self-designing machine.