1. A processing system executing multiple programs and operating under control of an operating system, the processor system comprising: a processor unit including: a dispatch/decode unit under control of the operating system for dispatching and decoding instructions of the multiple programs, the instructions each including a data ID; a plurality of execution units, each separately selectable by the operating system for receiving any of the instructions of the multiple programs from the dispatch/decode unit, wherein one of the execution units is executing an instruction from one of the multiple programs while another of the execution units is executing an instruction from another one of the multiple programs; and a retirement unit storing results of executed ones of the instructions uniquely in response to each data ID.