How UNIX spell ran in 64kB RAM

How do you fit a 250kB dictionary in 64kB of RAM and still perform fast lookups? For reference, even with modern compression techniques like gzip -9, you can't compress this file below 85kB.

In the 1970s, Douglas McIlroy faced this exact challenge while implementing the spell checker for Unix at AT&T. The constraints of the PDP-11 computer meant the entire dictionary needed to fit in just 64kB of RAM. A seemingly impossible task.

Abhinav Upadhyay

They still managed to do it, but had to employ some incredibly clever tricks to make it work, and make it work fast. Such skillful engineers interested in optimising and eeking the most possible performance out of underpowered hardware still exist today, but they're not in any position to make lasting changes at any of the companies defining our technology today. Why spend money on skilled engineers, when you can just throw cheap hardware at the problem?

I wonder just how many resources the spellchecking feature in Word or LibreOffice Writer takes up.