E.g., if you are writing code for a 68xx, you
have little choice
but to do everything in memory addressing.
Or a 6502. I don't know what to *do* with all the other registers on
other architectures. ^_^;;
For the exact opposite, look at the PERQ 1a at the microcode level. 256
general-purpose registers (each 20 bits wide). There's even an 8 bit
register which can be used to select a particular register -- that is
you have a sort of indirect addressing to the registers.
-tony