One of the most useful tools for a microcomputer laboratory is a development system for the implementation of a variety of microcomputers. Such a development system has been implemented for both 8 and 16 bit microprocessors such as the 8085, 8086, 68000, etc. The system incorporates not only the cross assemblers needed but common memory which can be downloaded from the CP/M system and can be tri-stated between the microcomputer in use and the CP/M system.