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Hard-wired Control Unit v/s Soft-wired Control Unit

written 6.6 years ago by sam.gas1998 • 0

modified 2.8 years ago by binitamayekar ★ 6.6k

what is the difference between hardwired and softwired contro unit?

computer organization and architecture

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written 2.8 years ago by binitamayekar ★ 6.6k

Hard-wired Control Unit v/s Soft-wired Control Unit

Sr. No.	Parameters	Hard-wired Control Unit	Soft-wired Control Unit
1.	Control Signal Generation	This unit generates the control signals needed for the processor using combinational logic units, featuring a finite number of gates.	This unit generates the control signals with the help of microinstructions stored in the control memory.
2.	Design	Its design is complex.	Its design is simplified.
3.	Approach	It is a circuit-based approach.	It is a programming-based approach.
4.	Architecture and Instruction Set	The architecture and instruction sets are not specified.	The architecture and instruction sets are specified.
5.	Main Processing Unit	It has a processor to create signals to be executed in the right sequence.	It facilitates the micro-sequencer from which instruction bits are decoded and executed.
6.	Speed	This unit is faster because the required control signals are generated with the help of hardwires.	This is slower because microinstructions are used for generating signals and also require frequent memory accesses.
7.	Flexibility in Modification	Modification is difficult as the control unit is hardwired and will require a change in hardware.	Modifications are easy as they will require the change in the code at the instruction level only.
8	Chip Area	It requires less area for chips.	It requires more area for the chip.
9.	Cost	More costly as everything has to be realized in terms of logic gates.	Less costly because only microinstructions are used for generating control signals.
10.	Complex Instructions	It cannot handle complex instructions as the circuit design for it becomes complex.	It can handle complex instructions.
11.	Instruction Set Size	It uses only a limited number of instruction sets due to the hardwired implementation.	Control signals for many instruction sets can be generated.
12.	Instruction Decoding	In this, it is very difficult to perform instruction decoding and sequencing logic.	In this, it is very easy to perform instruction decoding and sequencing logic.
13.	Control Memory	There is no control memory usage hence, no control memory is required.	This unit uses control memory hence, control memory is required.
14.	Method	It uses either mechanical or electrical ways to control things.	It always uses digital ways to control things. Means it has a computer or simpler table-driven calculator with software.
15	Error Occurrence	More prone to the occurrence of errors.	Less prone to the occurrence of errors.
16.	Applications	It is used in processors that use a simple instruction set known as the Reduced Instruction Set Computers (RISC).	It is used in processors based on a complex instruction set known as Complex Instruction Set Computer (CISC).
17.	Examples	CPU with hardwired control unit is Intel 8085, Motorola 6802, Zilog 80, any RISC CPUs, in a car the steering wheel, and Power Steering system.	CPU with microprogrammed control unit is Intel 8080, Motorola 6800, any CISC CPUs, and Today's fighter jets

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