I am a software developer with four years experience in .Net development, I always like to keep up to date with the latest technologies (.net related normally) being released and love learning them. I didn't however go to university and learnt all I know through helpful colleagues, .Net courses, the internet and good old books. I feel that I am a good developer, but without learning the lower levels of a computer as you would in the first year of a computer related Uni course, I get lost when talking to people about a lot of more technical lower level computing. Is there a book(s) that anyone could recommend, that would cover the lower levels of what is going on when I click "Run" in Visual Studio? I feel out of my depth when my boss says to me "Thats running in the CPU cache" or "you're limited by disk reads there", and would like to feel more confident when talking about how the hardware talks to each other (CPU to RAM etc).

Apologise if thats a vague question, or has been asked before (i did check and couldn't find anything on here that answers my question).