Chapters 3 and 4 made me remember of my uni classes:
Pretty much everything the chapters cover I have already studied or am studying right now.
But it was nice to review that stuff.

Chapter 3 is about computer architecture and organization.
Everything I know about this topic is because of a final project I did some time ago: I had to implement a simple ARM CPU.
The ALU, the datapath, the pipeline, the instruction cycle... everything I implemented in Verilog.
I have never implemented the CPU on a FPGA, I only simulated it using iverilog(1).
It was a fun project and one of the most challenging I have ever done.

Chapter 4 is about Operating Systems.
The reading of that chapter coincided with the reading of Tanenbaum's book on Operating System at my OS class.
I'm reading about processes and process scheduling right now, but I think those topics will be covered on the next chapter.