It's super easy to make an 8-bit computer with an arduino; just open the box and presto: You're holding an 8-bit computer ;-)
In the overview video I started to watch, he says the computer is based on the SAP-1 ("simple as possible") architecture from a text book. The first SAP-1 link I found was this (cad-sapreport.pdf)* which says that the 8-bit instructions are 4 bits opcode plus 4 bit immediate address, so if you expand the address space, this would have to change. Without having looked at details, it might be as simple as going to a 12 bit word length for the architecture, but if you change his architecture, you will have this sort of ripple effect**.Of course if you have 8 bit wide components, you can simply use 4 bits of them, but I think you're asking how you would expand the address space.* - For what it's worth there seem to be quite a few FPGA implementations of the architecture floating around the web.** - Some of the PIC microcontrollers use 8 bit data paths but wider instruction paths. That doesn't appear to be an option here because the SAP-1 uses a shared instruction and program memory architecture.
So in order for me to use a 8 bit memory address register I'll have to increase the number of address lines to 12 and almost everything else to 12? It is possible but I've already spent enough on parts on this project so If that's the case I'll just reduce the size of the memory address register down to 4, after work or course...
You'd have to increase the data path to 12 bits (i.e. memory width because it stores 12 bit instructions and probably the accumulator width as well). There would be 8 address lines instead of the current 4.Given that the processor is a demonstration of basic computer concepts rather than an implementation of a practical computing device, it seems expanding the memory space is a lot of extra work for little marginal benefit.