Prerequisite – Hardwired v/s Micro-programmed Control Unit
To execute an instruction, there are two types of control units Hardwired Control unit and Micro-programmed control unit.
- Hardwired control units are generally faster than microprogrammed designs. In hardwired control, we saw how all the control signals required inside the CPU can be generated using a state counter and a PLA circuit.
- A microprogrammed control unit is a relatively simple logic circuit that is capable of (1) sequencing through microinstructions and (2) generating control signals to execute each microinstruction.
|Hardwired Control Unit||Microprogrammed Control Unit|
|Hardwired control unit generates the control signals needed for the processor using logic circuits||Micrprogrammed control unit generates the control signals with the help of micro instructions stored in control memory|
|Hardwired control unit is faster when compared to microprogrammed control unit as the required control signals are generated with the help of hardwares||This is slower than the other as micro instructions are used for generating signals here|
|Difficult to modify as the control signals that need to be generated are hard wired||Easy to modify as the modification need to be done only at the instruction level|
|More costlier as everything has to be realized in terms of logic gates||Less costlier than hardwired control as only micro instructions are used for generating control signals|
|It cannot handle complex instructions as the circuit design for it becomes complex||It can handle complex instructions|
|Only limited number of instructions are used due to the hardware implementation||Control signals for many instructions can be generated|
|Used in computer that makes use of Reduced Instruction Set Computers(RISC)||Used in computer that makes use of Complex Instruction Set Computers(CISC)|