Comment by RiverCrochet

Worse, that would mean Arm64 is a 12-bit CPU. The original 32-bit ARM encoding could only load 8 bit immediates, though later versions gained a 16-bit load immediate instruction.

RISC-V is a bit better off, as it has a special encoding for 20 bit immediates, while Alpha and PowerPC are the same as MIPS, stuck with 16-bit immediates.

Ahh, but that would be mean because it would make ARM64 CPUs 16-bit too. Though actually if you put -1 and it sign-extends to 0xFFFF'FFFF'FFFF'FFFF then that's technically 64-bit? :p

the motorola 6809 can load 16 bit values into some of its registers but i've always seen it called an 8 bit CPU