An amazing thing about the TeX Book is that due to TeX's stability, it's mostly still current. It was written in a day when the graphical computer was a special thing that required a trip to the lab. So the stuff it has about how to run TeX is dated.

But once you know how to run TeX at your "site" (as they would have called it then) all the stuff on the language (that is, practically the whole book) is still good.