📝Number of CPU registers is primarily limited by ISA encoding size

source

Engheim₂₀₂₂ 29:00

The number of CPU registers is primarily limited by space to encode register number in ISA (more registers require more bits to encode register number). Number of transistors to add more registers is not an issue.

See also

• Registers may occupy significant portion of die size in very small processors. The above doesn’t seem to hold true for very small chips.