US Patent 7640418 Dynamic field patchable microarchitecture

A microprocessor memory architecture including a read-only memory (ROM) with programmed microcode and a random access memory (RAM) capable of storing microcode and one or more data bits used for the selection of corresponding ROM or RAM microcode for execution. A multiplexer receives input signals from both the ROM microcode and RAM microcode, and a control signal which is one or more RAM data bits is used to select from the RAM or ROM microcode inputs for further execution by the microprocessor.