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Difference between Mealy machine and Moore machine

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  • Difficulty Level : Easy
  • Last Updated : 19 Jul, 2022

Mealy Machine is defined as a machine in the theory of computation whose output values are determined by both its current state and current inputs. In this machine atmost one transition is possible. 
It has 6 tuples: (Q, q0, ∑, O, δ, λ’) 

  1. Q is a finite set of states 
  2. q0 is the initial state 
  3. ∑ is the input alphabet 
  4. O is the output alphabet 
  5. δ is the transition function that maps Q×∑ → Q 
  6. ‘λ’ is the output function that maps Q×∑→ O 

Prerequisite – Mealy and Moore Machines 

The diagram is as follows:

Moore Machine:

Moore machine is defined as a machine in the theory of computation whose output values are determined only by its current state. It has also 6 tuples

(Q, q0, ∑, O, δ, λ) 
  1. Q is a finite set of states 
  2. q0 is the initial state 
  3. ∑ is the input alphabet 
  4. O is the output alphabet 
  5. δ is the transition function that maps Q×∑ → Q 
  6. λ is the output function that maps Q → O 

Diagram:

The difference between the Mealy machine and Moore machine are as follows:

Moore Machine

Mealy Machine 

Output depends only upon the present state. Output depends on the present state as well as present input. 
If input changes, the output does change. If input changes, output also changes. 
More states are required. Less number of states are required.  
There is less hardware requirement for circuit implementation. There is more hardware requirement for circuit implementation.  
They react slower to inputs(One clock cycle later). They react faster to inputs.  
Synchronous output and state generation. Asynchronous output generation.  
Output is placed on states. Output is placed on transitions.  
Easy to design. It is difficult to design. 
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