> wonders how ARM did that

Acorn co-founder Hermann Hauser famously joked that he gave the original ARM microchip design team two distinct advantages: no time and no resources. With no money for a large crew or complex hardware, the tiny core team had to keep the processor design exceptionally simple, which ultimately birthed the revolutionary RISC architecture.

It also had to run in simulation on a BBC micro… Probably with a second processor via the Tube interface, but still.