The PIC instruction set refers to the set of instructions that a Microchip Technology PIC or dsPIC microcontroller supports. The instructions are usually programmed into the Flash memory of the processor, and automatically executed by the microcontroller on startup. PICmicro chips have a Harvard architecture, and instruction words are unusual sizes. Originally, 12-bit instructions included 5 address bits to specify the memory operand, and 9-bit branch destinations. Later revisions added opcode bits, allowing additional address bits.