A 180 GB game download that unpacks to 200 GB needs 380 GB of disk with a normal extractor, because at the worst moment the full archive and the full output exist at the same time. HatchZip — 1,692 stars in its first week on GitHub, v0.1.3 — claims to fix that by extracting from the end of the archive and truncating each finished part off the archive file as it goes, so "you only need free space for the output."

That's a falsifiable claim with a number attached, so I measured it. The catch, which took me three runs to find, is that the obvious way to measure it lies to you — and the tool's own space-saving only switches on when your disk is actually nearly full.

The test archive

I built the worst case for compression and the normal case for game downloads: 40 files of 20 MiB of pure random data (already-compressed assets behave the same way), zipped at level 1.

files: 40 × 20 MiB random + 1 directory = 41 entries uncompressed: 838.9 MB game.zip: 839,007,384 bytes (random data doesn't compress; the…