First an inverter is a box.. No motor, it does not make electricty, it converts the form of the power.
A generator has an engine, It burns fuel of some kind (Sunlight, Gasoline, Propane, Diesel, Wood, Coal, Falling water) and makes electricity.
Reading your original post I think you are talking about a
Traditional Generator or an Inverter GENERATOR
What is the difference?
Regular generators run at a constant speed. some sub multiple of 3600 RPM (3600 RPM 1800 RPM 1200RPM) and the power they generate is delivered. Some of these (epically the 3600RPM types) the power out is... .Kind of nasty (Looks like wholly catapiller on a scope trace)
Inverter genertators can run at most any speed. the power they generate is delivered not to you the user but to a box, called an inverter, which is built into the generator, This box outputs very nice clean power Pure sharp sine wave No "Fuzz" no spikes, sweetest power you will ever use.
And since the motor slows down when the load decreases and for other reasons (They are normally fully enclosed generators) they are fairly quiet.. in fact so quiet that some of the smaller sizes folks have gotten hurt thinking they were not running.. when they were.
You want that kind
How to tell what is being sold
Quick and dirty method.. A @@-####i (note the "i"_) is normally an inverter model
GOOGLE the model number and track it to the maker of the device, They know what they made. You can download the owner's manual there and read it.