what is the difference between creo parametric & autodesk inventor

The main deference is datums concept and more over the new commands like auto round and helical sweep is only available in creo parametric only.

I've used both extensively and these are my opinions:

1 - Creo manages large assemblies better. The mating contraints in Inventor is a separate feature outside the part, which is more cumbersome to correct when assembly orders change.

There is also a difference in that Creo seems to manage really RAM-consuming assemblies better. I've been told that this is due to the algorithms in the Granite kernel, blah blah, but I don't understand it.

I also like that Creo seems to share the memory space of a part with its representation in an assembly, so when you change a part the changes are simultaneously introduced in the assembly, rather than that you need to reload/rebuild the assembly parts again and again.

Brifly put: large assemblies are faster and doesn't fail as much in Creo as they do in Inventor.

2 - The sketcher in Creo is vastly superior. It guesses your design intent more clever, and after using Creo for a while, the Inventor sketcher feels really slow and dumb.

3 - Creo is rebranded Pro/Engineer, and Pro/E used to be extremely stringent. Harsh and unforgiving, some would say. This was actually a good thing, because it forced you to not be sloppy and do stuff that you would later regret. Creo has become a bit more forgiving, but I still prefer its strictness compared to Inventor - which for example allows you to reuse sketches from former features, causing havoc when you change an earlier sketch. Or makes faulty assumptions about sketch references.

PTC also have nicer licensing terms, or rather: "normal" licensing terms - whereas Autodesk won't allow you to install a version older than three years, and you have to pay service fees to be allowed to use older versions than the current one.

That said, the pros of Inventor are that the visualization is better - things look nicer, you can render fine pictures and movies of walkarounds. The rudimentary "PDM" functionality of Workspaces are a mixed bag - I prefer the Creo way of creating backups, but Inventor keeps a cleaner file structure.

Oh, and the 2D drafting mode of Inventor is far superior to that of Creo. Which is of little concern to me because making a good model is more important to me than putting it on paper.

So out of the two, Creo is overall the winner in my book. So much faster to work with, much less errors and problems. Although it is a bit stiff and old-timey.

The main difference is that anyone can download/install/authorize a free licence of Inventor to use for educational purposes, while the other packages need to be paid for this, although, they are similar - parametric, adaptive, a.s.o.