In processor design, microcode serves as an intermediary layer situated between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer, also known as its machine code. It consists of a set of hardware-level instructions that implement the higher-level machine code instructions or control internal finite-state machine sequencing in many digital processing components. While microcode is utilized in general-purpose CPUs in contemporary desktops, it also functions as a fallback path for scenarios that the faster hardwired control unit is unable to manage.
The microcode (and "nanocode") of the Motorola 68000 is stored in the two large square blocks in the upper right and the controlled by circuitry to the right of it. It takes up a significant amount of the total chip surface.
A central processing unit (CPU), also called a central processor, main processor, or just processor, is the most important processor in a given computer. Its electronic circuitry executes instructions of a computer program, such as arithmetic, logic, controlling, and input/output (I/O) operations. This role contrasts with that of external components, such as main memory and I/O circuitry, and specialized coprocessors such as graphics processing units (GPUs).
Inside a central processing unit: The integrated circuit of Intel's Xeon 3060, first manufactured in 2006
EDVAC, one of the first stored-program computers
IBM PowerPC 604e processor
Fujitsu board with SPARC64 VIIIfx processors