The invention relates to methods of simulation of a plurality of processors running on a plurality of cores, to multi-core microprocessor systems in which such methods may be carried out, and to computer program products configured to perform a simulation of a plurality of processors, running on a plurality of cores. According to a first aspect of the invention, there is provided a method of running a plurality of simulated processors on a plurality of cores, in which simulation of the processors is performed in parallel on the plurality of cores.