What's meant by this question?

"You need at least four states to exploit the advantages of a Mealy machine over a Moore machine."

I'm trying to wrap my head around this but I'm not sure "what" advantages are being spoken about. I know a 1 state Mealy Machine can have a possible 2 state Moore Machine. 2 state Mealy Machine can have a possible 3 state Moore Machine. etc...

  • 1
    \$\begingroup\$ That's not a question, it's a statement. And maybe if you told us a little bit about the context in which you found it, we could help you figure it out. \$\endgroup\$
    – Dave Tweed
    Dec 29, 2014 at 23:00

2 Answers 2


With a Moore state machine, the number of possible output combinations (I hesitate to say "output states") is no more than the number of internal states.

With a Mealy machine, the number of possible output combinations can be as high as the number of internal states multiplied by the number of input combinations.

Whether one is an "advantage" over the other really depends very much on context. For example, in high-speed logic design (such as an SDRAM controller), a Moore machine is preferred because the timing of the outputs is much more tightly controlled.

  • \$\begingroup\$ Decent explanation! \$\endgroup\$ Dec 30, 2014 at 2:02

Is this an exam statement (like a trick question or true/not true selection), because that's simply not true.

Consider this simplistic example: a Mealy machine with two states "Quiet" and "Talk" and an extra input signal "Message". The machine could be constructed such that when the machine is in the "Quiet" state, its output might remain at 0. And when in the "Talk" state, the output might be a copy of the "Message" input, allowing the message to be transmitted through the machine.

PS. The advantage of a Mealy machine over a Moore machine is that in the Moore machine, the outputs can only be dependant of the state, whereas in a Mealy machine, the outputs can be dependant of the state and the input(s). So the outputs of a Mealy machine can change whenever the inputs change, even if there is no change in state.


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