a parallel computer having a plurality of cluster buses 2 which are connected to the processor 1 via the selectors 6 . the selectors 6 maintain the same condition until the next instruction is received . in this system , the clusters 11 are reconstructed at appropriate timing during the operation of the processor , thus allowing the number of processors pes in a cluster to be exchanged in response to variation in the process load allocated to each cluster 11 . accordingly , the resources of the computer are used more effectively . the execution environment of each process may be independent . real time execution of each process can be assured .