Jason Knight thanks for the Niklaus Wirth book suggestion - I had never come across that recommendation even after a very exhaustive and extensive search last year all around the interwebs, so looking forward to check that out. I was given a CPC 6128 recently, and just ordered a CP/M Plus diskette, so looking forward to some assembly programming on that, like you say, a more manageable processor.

I am actually doing Nand2Tetris right now (I realised my answer could have been interpreted as if I have done it already, however my statement still stands). Definitely share your stories, and any questions or observations too. If you are interested, and you do end up doing nand2tetris, here is my nand2tetris github repo where I will be pushing files up as I do them: https://github.com/przet/nand2tetris I am up to the gate construction at the moment. I have previously done some study on this topic from the level above gates and hardware interpretation of command (so the software level) but I am hoping this will help solidify concepts.

Yeah, if you liked Code, I would definitely read it again, or continue reading it, and really try to understand it and absorb it. And yes Petzold answers your exact question!

Some great responses already. I would also highly recommend 'Code' by Charles Petzold and after that the Nand2Tetris companion book where you actually build a computer from gates up (on the computer using a Hardware Description Language). Building a computer yourself will probably be the best way to really know what is going on, especially after reading 'Code' and the other answers/sources here.