This book was my summer reading.
Maybe it's the good timing with my relatively new interest in electronics but this is one of the best technical books I have read. The author Chris Smith has reverse-engineered the ULA, the chip that handles the display, audio and i/o of the ZX Spectrum computer from the early 80's.
As an old assembly language programmer for the ZX Spectrum, I have had a basic understanding of what goes on in the circuits of a computer, but it was only through this book I understood how it actually works. It describes the inner workings of the ULA with timing diagrams and circuit drawings at a level that was just right. The only exception to this is that chapter 2 assumes familiarity with how semiconductors are constructed, which made me worry if I'd get through the book. Later chapters deal mostly with digital electronics and are approachable for an old-school programmer like me.
I learned a lot from this book and it inspired me to try to create my own very simple Z80 based computer: