Interesting. I remember the mainframes I worked on at Burroughs back in the 60's & 70's implemented the instruction set with a resistor-based read-only-memory about the size of a shoe box.

They definitely weren't anywhere close to zero boot time, but they were pretty fast. Burroughs had a firm patent on head-per-track hard drives that were deadly quick. Zero head seek time, just rotational latency. Average latency on the fastest was around 5 milliseconds! We just LOVED to do disk benchmarks against IBM (or anyone else).

A wee bit has happened since then. This stuff looks pretty cool. Wonder when we'll see it.