What's the difference between aten and c10?

What is aten?
And What is c10?
What’s the difference between aten and c10?
What’s the difference between cuda in aten and cuda in c10?

generally they are different namespace with different code using for different purpose. Can you make your question more specific?

What is the purpose of the two and in what way is it different?

It is hard to say in several sentences. we have both aten and c10 folder for legacy reason, it just because pytorch has a long history, code has been refactored multiple times. aten is older then c10, and at some point, we decide to move/refactor some of the core pytorch code into a new folder, so we create c10. Nothing special for both aten and c10, they just contains different pieces of pytorch code which is contributed at different time.