Donald was also writing at a time when all languages were close to the metal and optimization meant using various tricks (or writing critical portions in assembly) to improve performance.
And even caches. Though we called it "core", back then. Main memory was disk, tape, or drum, and cache misses caused page faults, if you were fortunate, or you had to roll in overlays yourself. Nowadays RAM is as inaccessible as disk was then, and you swap 64-byte pages, sometimes with network negotiations with remote (NUMA) cores, all in hardware.
That writing was 1974, Lisp had already existed.