This is a mistaken impression. Actually, microcode is not compiled. For any computer which is microprogrammed, there is a sequence of microinstructions which implements each executable statement of the computer. In the case of the Lisp machine (such as those built by Symbolics - like the 3600), the machine instructions are, in fact, the operators of Lisp. So, there is within the microcode of a List machine a sequence of microinstructions which implements directly the function of a Lisp operator, such as CAR. As it happens, it is easily possible for any of use to obtaine the so-called MacIvory, which is a Lisp machine that operates within the MacIntosh computer. It is a co-processor much like the i860 based board that I bought several years back from MicroWay. The i860 is a single chip implementation of the Cray-1, (you know, Harvard archetecture, and the like), and provides just about the same throughput as the Cray-1. An old high-school buddy of mine worked for Symbolics, and today does Lisp programming at Moffett Field for NASA Ames. He is quite well acquainted with the microcode of the 3600, and it is upon his instruction that I became equally familiar. William R. Buckley