A multiprocessor system with bus connections has a throughput which may be reduced significantly due to the bus conflict. One approach to ease this conflict is to group processors into a few clusters. This paper presents a clustered multiprocessor prototype called “MUGEN” and the systems software implemented. Its performance also is disusssed. As for the systems software, ext‐C and para‐C languages are introduced that are developed to express parallelism explicitly. Also, the par‐C preprocessor (P3C) that translates a standard C program into a parallel program written in para‐C is introduced. Finally, the Livermore loop results are presented to measure the performance.