1. Apparatus for processing data under control of program instructions from a first instruction set and one or more further instruction sets, said apparatus comprising: (i) an unhandled operation detector operative to detect unhandled operation of a program instruction of said first instruction set; and (ii) an unhandled operation handler operative upon detection of said unhandled operation to trigger emulation of said instruction of said first instruction set using one or more instructions of at least one of said one or more further instruction sets.