What is Micro Program Control Unit?

Answer 1

A micro program control unit is the underlying hardware that executes microcode. In turn, microcode is the code that is executed in order to process instructions, or code. In modern processors, an instruction is fetched from some area of memory (one or more bytes of memory), and is then parsed and executed by microcode. Microcode runs on the various gates and transistors that comprise the CPU.

One might consider microcode to be the operating system ("OS") of the CPU, just as Windows, Linux, Android, etc, is consider the OS of the computer. Microcode allows a standard chipset to be programmed in different ways, altering its behavior completely. Optimizing microcode results in certain operations taking less or more time, allowing the same basic chip hardware to be specialized for certain types of tasks, such as favoring mathematical calculations or memory processing.

Intel and AMD both offer "IBM-compatible" processors that expose the same set of instructions, but their microcode is different and reflects different interests in processing. Different iterations of the same chipset can be released that offer different characteristics without modifying the actual hardware.

Furthermore, hardware-based designs (e.g. circuit programming) is relatively difficult and error-prone as compared to microcode programming. A mistake in microcode can be corrected simply by altering the code, while a mistake in a hardware design might require significant time and cost redesigning the entire circuit.