Mine was never an exercise in practicality - it would be ridiculous to implement, and complete overkill.

OTOH, I wonder if someone would build something like this - a 6502/65816 with lots of SRAM and system-bus compatible timings - using the cheapest commercially available foundry, how much could it cost.

Dream big. Imagine what we could do with a 5 GHz 6502.

Of course, the memory would need to be on the same die to be able to function at that speed, but my Apple //e had a full megabyte of RAM (in addition to the 64 on the motherboard) and, IIRC, Apple’s bank switching scheme could accommodate up to 16 megs. The chip would be mostly SRAM.

Talking to anything outside the chip would slow things down considerably though, and using one in place of a real 6502 would be comically weird. It’d feel like a machine that spends 99.999999% of the time waiting for IO.

Which, amusingly, feels the opposite of mainframes, where the machine appears to never have to wait for IO.

The first time I used an IBM PC I was so disappointed. On every aspect of the interaction my Apple II would run rings about it. Character IO via the BIOS on CGA was glacial to avoid writing to VRAM and getting snow, and an 8088 at 4.77 MHz was not nearly 4.77 times faster than the 6502 at 1 MHz - in fact, it felt slower.

It’s not that the 8088 was a horrible CPU - it was a pretty ok one - it’s just that the 6502 was a beast of a CPU.

Also https://news.ycombinator.com/item?id=48068333, but got little traction.