The collection of machine language instructions that a particular micro-processor understands. The term is largely synonymous with “instruction set architecture” or ISA, i.e., the parts of a processor’s design that need to be understood in order to write assembly language, such as the machine language instructions and registers. Many aspects of instruction sets may be proprietary, i.e., covered by patents or only disclosed in a know-how license. The best-known instruction sets are the Intel’s X-86 set and the ARM set.