Before you click that magnet link or YouTube description URL, run this mental checklist:
Standard compression algorithms (like ZIP or 7z) can only reduce a 3GB ISO by a few hundred megabytes because system files and images (JPEGs/icons) are already partially compressed. How to make compressed iso images? - Super User 22 Dec 2012 — highly compressed windows 7 iso file
Often stripped of heavy background processes. How Compression Works Before you click that magnet link or YouTube