Genera ran on actual Lisp machines, I feel that that is not a fair comparison.
It's not exactly hidden knowledge that the Intel compilers produce the best code, it's just that they have draconian licensing requirements. Furthermore, that knowledge cannot possibly be lost, because they're still actively developed to this day. I'm interested in the technological specifics of what these older platforms did that the newer ones cannot do, and why the knowledge of how to do them has been lost.
It's not exactly hidden knowledge that the Intel compilers produce the best code, it's just that they have draconian licensing requirements. Furthermore, that knowledge cannot possibly be lost, because they're still actively developed to this day. I'm interested in the technological specifics of what these older platforms did that the newer ones cannot do, and why the knowledge of how to do them has been lost.