Ask HN: Best resources to learn low-level programming?

I have always developed in the web contest, and rarely I have needed to deal with files/bytes... Now I am in this position, and I need to learn Go. Go seems really good to me, and has good resources, but when it comes to int64, float32, arrays of bytes.... I find my self overwhelmed.

Is there any resource that explain in a clear way this concepts?? If it s a Golang related resource even better.