Micro programmed and Hardwired control unit

The Micro programmed and Hardwired control unit generates the control signals to fetch and execute instructions. The fundamental difference between these units is that hardwired is a circuitry approach whereas, the microprogrammed control unit is implemented by programming.

Micro programmed control unit:
A control unit with its binary control values stored as words in memory is called as microprogrammed control. Each word in the control memory contains microinstruction that specifies one or more micro-operations for the system. A sequence of microinstructions constitutes a microprogram.

Hardwired Control Unit:
When the control signals are generated by hardware using conventional logic design techniques, the control unit is said to be hardwired. The hardwired control unit is designed for the RISC style instruction set. On the other hand, the microprogrammed control unit was designed for the CISC style instruction set.

Comparison Chart

Basis	Hardwired Control Unit	Microprogrammed Control Unit
Basic	It is a circuitry approach.	This control unit is implemented by programming
Design	RISC style instructions	CISC style instructions
Modification	Modification is difficult as the control unit is hardwired. Modifying it will require the change in hardware.	Modifications are easy in case of the microprogrammed control unit as it will require a change in the code only.
Instructions	It works well for simple instructions.	It works well for complex instructions also.
Costing	Implementing a hardwired structure requires a cost.	Implementing microprograms is not costly.
Control memory	No control memory is required	Control memory is required
Execution Speed	Faster execution	Comparatively slow

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