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Yup, and early TeX did it too. You could run a memory dump of a previously initialized version to improve start-up times.

For a modern take on similar idea see also this discussion from a while ago:

"Improving startup time in Atom with V8 snapshots"

I stole that idea from the 1970's FORTRAN program ADVENT, the precursor to Zork.

I was amazed that I never ran across another DOS program that used the technique.

there's also unfork(2)!

Do you unfork then unexec or unexec then unfork?