Imagesource: https://howcpuworks.com/

One of the significant advantages of our beloved 8-bit technology is that most of its hardware incarnations and instruction sets are relatively simple. This simplicity allows one to fit a comprehensive understanding snugly within the narrow confines of one's mind.

Interestingly, modern processor design, especially with RISC-V, seems to be reverting back to very reduced ISAs and relatively simple architectures. For those wanting to learn how to build a CPU from scratch today, a RISC-V architecture is by no means a poor choice — especially given the number of 8-bit candidates available.

For those who wish to tread a different path and understand everything at the transistor level, there's a wealth of materials available, in the form of readings or YouTube videos. Now, an online book has been added to that mix:

How a CPU works is still a work in progress, but currently boasts four completed and notably interactive chapters.

The, unfortunately, unknown creator uses Paul Falstad's circuitjs library to animate the key concepts. Testing one's own knowledge (or lack thereof) in the initial four chapters is genuinely enjoyable.

We can only hope the remaining content is soon fleshed out, giving life some final purpose. 😁