1. A computer processor having control and data processing capabilities comprising: a decode unit for decoding instructions; a data processing facility comprising a first data execution path including fixed operators and a second data execution path including at least configurable operators, said configurable operators having a plurality of predefined configurations, at least some of which are selectable by means of an opcode portion of a data processing instruction; wherein said decode unit is operable to detect whether a data processing instruction defines a fixed data processing operation or a configurable data processing operation, said decode unit causing the computer system to supply data for processing to said first data execution path when a fixed data processing instruction is detected and to said configurable data execution path when a configurable data processing instruction is detected.