I don't recall anything about CPUs in SICP. Its more about data driven programming and writing of intepreters.

What i liked about SICP and scheme programming was that it is a pretty good environment for tinkering - the REPL makes it easy to combine functions, and to work in a bottom-up manner. (btw you had less of that in common lisp, and most other environments that teach you to work in a top down way, however you can still work with the Python REPL).

Maybe this bottom-up approach is what Sussman really has in mind when he is talking about first principles, because SICP is really not about working up from the atoms to the scheme interpreter/compiler.