Real-time simulation has been used since the early days of computer simulation. Current real-time operating systems can support real-time simulations with frame times as short as hundreds of microseconds. Some applications are now emerging that need shorter frame times, as low as 1 microsecond. New techniques are required for these high-speed real-time (HSRT) simulations. One approach is based on small arrays of digital signal processors. For complex systems it may be necessary to embed HSRT simulations in a larger real-time system using a multi-rate approach.