[lispm]

They were not that conventional. The first Lisp Machines were using micro-coded processors with special instruction sets tailored for compiled and interpreted Lisp.

* tagged architecture

* stack-oriented architecture with large stack buffers

* hardware assisted GC

* support for generic Lisp operators. For example a simple + operator.

* support for basic Lisp data structures like cons cells

The result is that Lisp programs compile to very compact machine code.

[ANTSANTS]

I'm guessing that by "far more radical" the GP meant "directly evals s-expressions." Especially since, IIRC, that's how PicoLisp works. I don't think there is much benefit to that approach over simpler register machines, but it's an interesting idea at least.