1. In a microprogrammed data processing system including high level instruction storage means, the combination comprising: task generation means for fetching high level instructions from said high level instruction storage means and in response thereto generating one or more tasks for performing each high level instruction, each task being in turn performable by the execution of one or more task microinstructions; microinstruction storage means for storing selectably addressable task microinstructions for use in performing said tasks; said task generating means being operative to access selected microinstructions from said microinstruction storage means; microinstruction execution means for receiving and executing microinstructions selected from said microinstruction storage means by said task generating means; and task control means responsive to said task generation means and to said microinstruction execution means for determining which tasks are ready for execution and for causing said task generation means to address said microinstruction storage means with addresses corresponding to ready task microinstructions, the order of addressing of microinstructions being chosen to allow for the execution of ready task microinstructions by said microinstruction execution means in an intermixed order regardless of the particular task to which each belongs so as to thereby provide for task multiprogramming at a microinstruction level.