[en] The development of a general purpose computer system, THESEUS, is described the initial use for which has been magnetic field analysis. The system involves several computers connected by data links. Some are small computers with interactive graphics facilities and limited analysis capabilities, and others are large computers for batch execution of analysis programs with heavy processor demands. The system is highly modular for easy extension and highly portable for transfer to different computers. It can easily be adapted for a completely different application. It provides a highly efficient and flexible interface between magnet designers and specialised analysis programs. Both the advantages and problems experienced are highlighted, together with a mention of possible future developments. (U.K.)