HN is written in a lisp variant and most the stack is built in-house , it is not difficult to imagine efficiency improvements when many abstraction layers have been removed from your stack .
What I do remember, is that it was a social data collection experiment for a couple of social scientists, that never originally expected that many people would actually find ways to find each other and hook up using it.
I miss their old findings reports about how weird humans are and what they lie about. Now, it's just plain boring with no insights released to the public.
Nick carver from SO also one mentioned that they could run SO if a single server , while it wasn’t fun it was doable and had happened some time .