The requirements for training systems for increasingly sophisticated aircraft continue to extend the technology of computing systems applied to real-time simulators. This paper describes a distributed computing system, partitioned on a functional basis with the autonomous major functions connected as a network. This system, called Functionally Distributed Simulation, is the basis for a new simulator generation, the Micro Simulation Technology (MST) simulator. It permits designing and manufacturing a simulator on a modular basis, which achieves considerable advantages in life-cycle costs, especially those associated with maintenance and upgrades. Microprocessors are used throughout, to achieve even greater flexibility and reliability. Extensive use is made of parallel processing to meet the high iteration rates needed for simulators; the various ways of interconnecting the microprocessors to meet the performance requirements are described. Microprocessors are also used for dedicated tasks such as real-time status monitoring and built-in test features, especially within the integral distributed input/output system. The performance of this system is described, together with results from simulators that use this modular approach.