[en] A functional simulation of te PDP-11 series minicomputers was implemented to run either interactively or as a batch job on an IBM 370 computer. The simulator operates in two modes, the supervisor mode and the run mode. In the supervisor mode, the simulator implements a command language, which allows users to examine and change the contents of memory or other addressable registers in the simulated machine. Optionally, an instruction trace may also be turned on or off. In the run mode, the simulation of the instruction set is tested by successfully running DEC's MAINDEC basic instruction test on the simulated machine. The interrupt structure is modeled. The simulation is open ended in the sense that users may define new peripheral devices, by including their own FORTRAN callable subroutines for each simulated device. Currently the following devices are supported: floppy disks, a console terminal, a card reader, a card punch, a line printer, and a communications multiplexer (DH11). With these devices DEC's RT-11 versions 2C and 3B have been successfully run on the simulator. At SLAC this simulator is proving useful in debugging software for one-of-a-kind hardware configurations, such as communications front end processors, that are not readily accessible for stand alone testing. 5 figures