What is the primary architectural advantage of a Microprogrammed Control Unit over a Hardwired one?
Ease of instruction set updates
The control unit of a CPU generates the sequence of control signals that direct every micro-step of instruction execution.
A hardwired control unit builds this logic directly from fixed gates, flip-flops and combinational circuits, so its behaviour is frozen into the hardware.
Changing or extending the instruction set in a hardwired design therefore means physically redesigning the circuitry, which is slow and expensive.
A microprogrammed control unit instead stores the control signals as microinstructions in a special control memory, so the machine's behaviour is defined in firmware rather than in fixed wiring.
Because the instruction set can be changed simply by rewriting the microprogram, the primary architectural advantage is Ease of instruction set updates.
Hardwired control is actually faster because signals come straight from logic gates, and it can use fewer gates and less power, so faster execution, lower power and reduced gate count are strengths of the hardwired design, not of the microprogrammed one.
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