In documentation I can see whats new about new features or commands but I cant find what has been changed in the "core" of the program in order to improve performance. Where can I find information about it? Any feature has been rewrited to take advantage of multiple processor cores?
Glad you taking a look at the new Release!
We don't generally include comments in the What's New about the internals of NX, but usually focus on the things the customer actually sees.
There is a recent example, however, of the case you are asking about, and since it's one that was new in 12.0.2 we often include it when talking to customers about the latest Release because many of them have not seen 12.0.2 yet.
As you'll see here, it does point out that part of the benefit of Minimal Load comes from "... makes use of multi-core processors to improve load performance".
We are looking for areas where this sort of technology will benefit users, but we don't "re-write" functions just for the sake of saying we "take advantage of multiple cores", because doing so does not always mean better performance (and in some cases, can even make it worse). Same goes for making better use of GPU, cloud computing, pre-computing, and other new technologies.
In some cases, you may just see benefits (faster performance) without us mentioning the specific technology behind it, and in others, like Minimal Load, we'll explicitly point it out.
We look forward to hearing about your experience.