A processor, comprising: a decoder that translates a plurality of standard macroinstructions of a predetermined instruction set architecture into microinstructions of a predetermined native instruction set of the processor and that forwards said microinstructions to an execution system with predetermined executing functions; wherein said decoder forwards a received user-defined instruction, UDI, load instruction to a UDI loader, wherein said UDI load instruction specifies a UDI macroinstruction and an address of a memory location of programming information; a programmable execution unit, PEU, that comprises a plurality of programmable logic elements and a plurality of programmable interconnectors that are collectively configured to be programmed to perform at least one processing operation; an instruction table that is programmable to include at least one UDI macroinstruction and at least one UDI microinstruction that corresponds with each of said at least one UDI macroinstruction; a UDI handler, wherein said decoder forwards a received UDI macroinstruction to a said UDI handler; and wherein said UDI loader is responsive to said UDI load instruction to program said instruction table with said specified UDI macroinstruction, and wherein said UDI loader retrieves said programming information and programs said PEU to perform a corresponding processing operation in response to said specified UDI macroinstruction, wherein said PEU is programmed to perform a plurality of processing operations, each for a corresponding one of a plurality of UDI macroinstructions programmed into said instruction table, and each of a plurality of different processes is identified by a corresponding one of a plurality of process identifiers, and each entry of said instruction table for each of said plurality of UDI macroinstructions is programmed with a corresponding one of said plurality of process identifiers; and said UDI handler determines whether said received UDI macroinstruction is programmed in said instruction table as said specified UDI macroinstruction, and if so, forwards said corresponding at least one UDI microinstruction to said PEU to perform said corresponding processing operation. a decoder that translates a plurality of standard macroinstructions of a predetermined instruction set architecture into microinstructions of a predetermined native instruction set of the processor and that forwards said microinstructions to an execution system with predetermined executing functions; wherein said decoder forwards a received user-defined instruction, UDI, load instruction to a UDI loader, wherein said UDI load instruction specifies a UDI macroinstruction and an address of a memory location of programming information; a programmable execution unit, PEU, that comprises a plurality of programmable logic elements and a plurality of programmable interconnectors that are collectively configured to be programmed to perform at least one processing operation; an instruction table that is programmable to include at least one UDI macroinstruction and at least one UDI microinstruction that corresponds with each of said at least one UDI macroinstruction; a UDI handler, wherein said decoder forwards a received UDI macroinstruction to a said UDI handler; and wherein said UDI loader is responsive to said UDI load instruction to program said instruction table with said specified UDI macroinstruction, and wherein said UDI loader retrieves said programming information and programs said PEU to perform a corresponding processing operation in response to said specified UDI macroinstruction, wherein said PEU is programmed to perform a plurality of processing operations, each for a corresponding one of a plurality of UDI macroinstructions programmed into said instruction table, and each of a plurality of different processes is identified by a corresponding one of a plurality of process identifiers, and each entry of said instruction table for each of said plurality of UDI macroinstructions is programmed with a corresponding one of said plurality of process identifiers; and said UDI handler determines whether said received UDI macroinstruction is programmed in said instruction table as said specified UDI macroinstruction, and if so, forwards said corresponding at least one UDI microinstruction to said PEU to perform said corresponding processing operation.