Control unit generates timing and control signals for the operations of the computer. The control unit communicates with ALU and main memory. In this lesson, you will learn how microprogramming and hardwired control sets are designed in computer architecture. You will be able to describe. The main difference between Hardwired and Microprogrammed Control Unit is that a Hardwired Control Unit is a sequential circuit that.

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We can use any large FSM, that has horizontal microcode like state assignment, since the delay for the FSM does not matter at all so long as it is less than or equal to the delay for the data-path that includes adders, shifters and so on, since the FSM works in parallel with the data-path.

Hardwired Control Unit is implemented using various electronic components such as combinational logic miccroprogrammed and gates. The idea of microprogramming was introduced by Maurice Wilkes in as an intermediate level to execute computer program instructions.

Difference Between Hardwired and Microprogrammed Control Unit

The pair of a “microinstruction-register” and a “control storage address register” can be regarded as a “state register” for hardwired control. Moreover, it is difficult to perform instruction decoding in Hardwired Control Unit than in Microprogrammed Control Unit.

On some processors, the Control Unit may be further broken down into additional units, such as an instruction unit or scheduling unit to handle scheduling, or a retirement unit to deal with results coming from the instruction pipeline. The algorithm for the microprogram control unit,unlike the hardwired control unit, is usually specified by flowchart description. The CU receives external instructions or commands which it converts into a sequence of control signals that the CU applies to the data path to implement a sequence of register-transfer level operations.


It tells the computer’s memory, arithmetic and logic unit and input and output devices how to respond to the instructions that have been sent to the processor. Outputs of the controller are organized in microinstructions and they can be easily replaced.

Control unit

Basic Structure of the Computer. As compared to some s or s computers without a proper CU, they often required rewiring their hardware when changing programs. This results in a computer that could run a complete program and require no human intervention to make hardware changes between instructions as had to be done when using only punch cards for computations before stored programmed computers with CUs were invented. More precisely, the Control Unit CU is generally a sizable collection of complex digital circuitry interconnecting and directing the many execution units i.

Their design uses a fixed architecture—it requires changes in the wiring if the instruction set is modified or changed. A control variable refers to a binary variable that specifies micro-operations.


In Microprogrammed Control Unit, modifications can be implemented by changing the microinstructions in the control memory. Leave a Reply Cancel reply. The Control unit CU is digital circuitry contained within the processor that coordinates the sequence of data movements into, out of, and between a processor’s many sub-units.

These microinstructions refer to a control word that resides in control memory, containing control signals for execution of micro-operations. The second English paper introducing horizontal microcode like state assignment for an FSM. In conclusion, the main difference between Hardwired and Microprogrammed Control Unit is that a Hardwired Control Unit is a sequential circuit that generates control signals while a Microprogrammed Control Unit is a unit consisting of microinstructions in the control memory to generate control signals.

Difference Between Hardwired Control and Micro programmed Control Unit. » Tutorial Bazar

A control word is a set of ones and zeros in a control variable. On the other hand, Microprogrammed Control Units are easier to modify, decode, implement and capable of handling complex instructions. Tomasulo algorithm Reservation station Re-order buffer Register renaming. As it is hardwired, the instruction set is microprogrammev and does not change.


To do modifications in a Hardwired Control Unit, the entire unit should microprkgrammed redesigned. The result of these routed data movements through various digital circuits sub-units within the processor produces the manipulated data expected by a software instruction loaded earlier, likely from memory. This is a truth table. The processor or the CPU is the main component of the computer that handles most of the tasks.

This article is microprogrammd the component of a computer’s CPU. We can assign any 0,1 values to each output corresponding to each address, that can be regarded as the input for a combinational logic circuit.

It consists of main two subsystems: This CU instruction decode process is then repeated when the Program Counter clntrol incremented to the next stored program address and the new instruction enters the CU from that address, and so on till the programs end.

Branch prediction Memory dependence prediction. Hardwired control also can be used for implementing sophisticated CISC machines.

Cotrol processing unit Digital electronics. Data dependency Structural Control False sharing. The Control Unit can either be hardwired or microprogrammed. Hardwired Control Units are difficult to modify, decode and implement, but executes operations much faster.

Retrieved from ” https: The hardwired approach has become less popular as computers have evolved.

Note that a control storage can be regarded as a combinational logic circuit. Hardwired control units are generally faster than microprogrammed designs. Therefore, Microprogrammed Control Unit is more flexible. This page was last edited on 20 Decemberat