@RiscIn2022
There’s a small mistake: for 64 registers you need 6 bits to address one, not 7 so 3*6=18 not 21..
If memory serves the Alpha had 64 64bit registers.
Oops, thanks for the math correction.
https://devblogs.microsoft.com/oldnewthing/20170807-00/?p=96766 and https://en.wikipedia.org/wiki/DEC_Alpha both say Alpha had 32 registers though.
Later: confirmed it had 32 GPR’s, though it also had 32 floating point regs so that may be what you were thinking of.