Abstract: A direct-execution microprogrammable microprocessor system uses an emulatory microprogrammable microprocessor for direct execution of microinstructions in main memory through a microinstruction port. A microinstruction cache with a microinstruction address extension unit serving to communicate microinstructions from the main memory to the microprogrammable microprocessor. Virtual main memory accesses occur through a system multiplexer. A virtual address extension unit and a virtual address bus provide extension and redefinition of the main memory address space of the microprogrammable microprocessor. The system also uses a context switching stack cache and an expanded address translation cache with the microprogrammable microprocessor having a reduced and redefined microinstruction set with a variable microinstruction cycle.