My point is that after reading the book I kind of knew how I could implement a simple CPU in real HW (with ALU, memory, etc.) but it was not clear to me how the IO part (kbd, screen) would work. Is the kbd connected directly to a certain place of memory? How is this implemented? Would there be some screen/gpu HW that is directly connected to the memory region? How is the CPU clock involved?

E.g. if you press a key, hold it and then release it, it is possible that this event gets missed as it was too short and the key press method did not check the memory region at the right point of time. For me their implementation enforces this bogus "I am in total control of everything that happens feeling" which often leads to bad design as it ignores the messy real world. I would have appreciated something more sophisticated and generic there which would work for different kinds of HW. Maybe I am missing some simple bus-system one might say ...

Nevertheless it is a wonderful book and I had lots of fun with it! :)