Ask HN: Resources for a poser programmer?

Hey all,

I've studied programming before. CS was my minor at University, and I've dabbled in several languages since graduation. I've almost exclusively dealt in interpreted languages.

But I don't feel I have a firm grasp on computer science fundamentals. Not just algorithms, but lowqer level issues, like stack vs. heap, process and thread management, garbage collection/memory management, etc.

What are your recommendations for accessible introductions to systems programming?