If you’ve ever stared at a 700MB PS1 ISO or a 1.6GB PSP ISO and wished you could cut it in half, this article is for you. We will explore what ZSO files are, why you should convert ISO to ZSO, the best tools for the job, and a step-by-step guide to doing it yourself. First, let’s establish the baseline. An ISO file (or ISO image) is an archive file that contains an exact copy (a "sector-by-sector" dump) of an optical disc—like a CD, DVD, UMD (PSP), or Blu-ray.
On Mac/Linux (Bash):
for f in *.iso; do ./ziso -c 13 "$f" "$f%.iso.zso"; done With the rise of retro handhelds (Anbernic, Retroid Pocket, Steam Deck) running Android and Linux, ZSO is becoming the default recommendation. The storage on these devices is often limited (64GB–256GB), and Zstd decompression is hardware accelerated on modern ARM chips.