What is the primary architectural advantage of a Microprogrammed Control Unit over a Hardwired one?

Question

What is the primary architectural advantage of a Microprogrammed Control Unit over a Hardwired one?

1. A. Ease of instruction set updates (Correct answer)
2. B. Faster execution speed
3. C. Lower power consumption
4. D. Reduced physical gate count

Correct Answer

Option A — Ease of instruction set updates

Detailed Solution & Explanation

The correct answer is Ease of instruction set updates.

Key Points

• A Microprogrammed Control Unit stores its control logic as microinstructions in control memory, so modifying or extending the instruction set means rewriting that microcode rather than redesigning hardware.
• That flexibility is its defining advantage.
• A Hardwired control unit implements the logic in fixed circuitry, which makes it faster, more compact and typically lower in power — so the other three options describe hardwired strengths, not microprogrammed ones.

Additional Information

• The trade-off maps onto processor design philosophy: CISC processors, with large and complex instruction sets, generally use microprogrammed control, while RISC processors with small regular instruction sets favour hardwired control for speed.
• Microprogramming was introduced by Maurice Wilkes in 1951.
• Because the microcode is stored, a design fault can sometimes be corrected by a firmware update rather than replacing silicon — a practical consequence of the same flexibility.
• The control unit and the ALU together with registers make up the CPU.