Yes, some were microcoded. And you were able to replace that microcode with your own creations! See for example this paper, where they took a VAX and rewrote i

Yes, some were microcoded. And you were able to replace that microcode with your own creations! See for example this paper, where they took a VAX and rewrote its microcode so that it executed instructions for the Warren Abstract Machine, the output format of their Prolog compiler. It's like you would reprogram your Core i7 to directly consume JVM bytecode. http://hps.ece.utexas.edu/pub/gee_micro19.pdf http://hps.ece.utexas.edu/pub/gee_micro19.pdf