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Welcome to my complete documentation for the ISO Compressor tool! Everything you need to know about installation, compression formats, and hardware setup is below.
Welcome to the ISO Compressor wiki! I built this tool to make compressing PS1, PS2, and PSP backups as effortless as possible.
The easiest way to use this tool on macOS is with the drag-and-drop GUI.
-
Download: Go to the Latest Releases page and download
ISO_Compressor_Mac.zip. -
Extract: Unzip the file to get the
ISO Compressor (Mac).app. (You can place this in your Applications folder or Desktop). -
Usage:
- You can simply double-click the app to open it and select a file.
- OR, you can drag-and-drop your
.iso,.cso, or.cuefile directly onto the app icon!
- Select Format: A window will pop up asking which format you want to compress into (CHD, CSO, ZSO). Pick the correct one for your emulator or hardware.
- Auto-Updates: When you launch the app, it will silently check for updates. If a new version is out, it will ask if you want to download it automatically.
Note on PS1 Games: If your PS1 game has multiple
.binfiles and one.cuefile, make sure they are all in the same folder. Only drag and drop the.cuefile onto the app!
If you prefer using the command line, or if you are on Windows or Linux, I built a fully interactive Terminal User Interface (TUI).
macOS:
curl -sL https://github.com/wako69420/iso-compressor/releases/latest/download/install_mac.sh | bashLinux:
curl -sL https://github.com/wako69420/iso-compressor/releases/latest/download/install_linux.sh | bashWindows (PowerShell):
irm https://github.com/wako69420/iso-compressor/releases/latest/download/install_win.ps1 | iexOnce installed, simply type the following command into your terminal:
iso-compressorThis will launch the interactive menu where you can drag and drop files directly into your terminal window!
When dealing with massive game backups, choosing the right compression format is critical. This tool explicitly outputs three distinct formats, each tailored for a specific use case.
Best for: Emulators on PC/Mac/Mobile (DuckStation, PCSX2, RetroArch) Format Supported By: Emulators only. Real hardware cannot read CHD natively.
CHD is the absolute gold standard for CD and DVD-based game preservation. It uses extremely advanced, multi-layered lossless compression:
- LZMA / zlib: Used to aggressively shrink standard game code and data.
- FLAC: Used to perfectly compress raw CD-Audio tracks (which is why it is flawless for PS1 games).
On average, compressing a standard ISO or BIN/CUE folder into a CHD will cut your file size almost in half. The exact savings depend heavily on how the original developers built the game:
-
Dummy-Padded Games: In the 90s, developers often stuffed blank "dummy data" onto PS1 and PS2 discs to push the actual game code to the outside edge of the physical CD (which spun faster, reducing load times). CHD completely obliterates these blank files. A 700MB
.binfull of dummy data might shrink down to just 150MB. - Audio-Heavy Games: Games that are mostly CD-Audio (like Wipeout or Tomb Raider) shrink beautifully because the FLAC algorithm cuts audio sizes by 50% without losing a single drop of quality.
- Video-Heavy Games: Games packed with pre-rendered FMV cutscenes (like Final Fantasy VII) shrink the least (around 20%), because the video files on the disc were already heavily compressed by the original developers.
Because CHD is so complex, a real PS1 or PS2 processor is not powerful enough to decompress it on the fly. However, modern PCs and phones can decompress it instantly, making it the perfect format for emulation.
Best for: PSP Emulation (PPSSPP) and Legacy PSP Hardware (PRO/ME CFW)
CSO is the classic compressed format that has been around for over a decade. It utilizes standard Zlib compression.
- The Pros: It has near-universal compatibility with all legacy PSP Custom Firmwares and shrinks files incredibly well.
- The Cons: Zlib compression is very tight, meaning it requires significant CPU power to unzip. On modern PCs (using PPSSPP), this is unnoticeable. But on a physical PSP, the weak CPU chokes while trying to decompress heavy games (like God of War or GTA), leading to severe lag spikes and audio stuttering.
Best for: Real Physical Hardware (PSP via ARK-5 / PS2 via OPL)
ZSO is the modern replacement for CSO when playing on real hardware. Instead of Zlib, it uses the LZ4 compression algorithm.
- Why it's better for hardware: LZ4 does not compress the file quite as small as Zlib, but it decompresses up to 500% faster.
- This means the ancient processors inside the PS2 and PSP can effortlessly unpack the game code in real-time, completely curing the lag spikes and stuttering associated with CSO files, while still saving you massive amounts of space!
If you have a massive library of games, doing them one by one is tedious.
The new GUI and TUI apps feature Batch Folder Compression. Simply drag and drop an entire folder of .iso, .cso, or .cue files into the app. It will automatically group them, verify the formats, and compress all of them sequentially while you step away!
If you are new to PS1 emulation, you might be wondering why your PS1 games download as a messy folder full of multiple .bin files and one tiny .cue file, instead of a single .iso file like PS2 or PSP games.
Here is the breakdown of how PS1 formats actually work, and why CHD is the ultimate solution.
The .iso format is physically incapable of holding multiple tracks. It can only hold standard computer data.
PS1 games, however, are essentially just interactive music CDs. A PS1 disc usually has one "Data Track" (the actual game code) followed by multiple "CD-Audio Tracks" (the background music).
If you rip a PS1 game to .iso, all of the CD-Audio music tracks get permanently deleted because the format can't store them. If you play that .iso, you will play the game in dead silence (no background music). Because of this, nobody uses .iso for PS1 games.
The undisputed standard format for PS1 games is .bin and .cue.
-
.binfiles: These contain the actual raw data (the game code and the raw music audio). -
.cuefile (Cue Sheet): This is a tiny plain-text map. It tells the emulator exactly where the game data ends and where the music tracks begin so the soundtrack plays correctly.
Having 15 .bin files for a single game is a cluttered mess. My tool fixes this using the chdman engine.
When you want to compress a PS1 game, you simply drag and drop ONLY the .cue file into the tool. (Make sure all the .bin files remain in the exact same folder).
Here is what happens in the background:
- The compression engine opens the tiny
.cuemap. - It reads the names of all the
.binfiles and automatically pulls all of them in from the surrounding folder. - It seamlessly stitches all the game data and music files together, applies heavy FLAC and LZMA compression, and spits out a single, unified
.chdfile.
You get to keep all the CD-quality music, but it takes up 40% less space and reduces your messy folder down to just one perfect file!
If you intend to play your compressed games on actual, physical retro consoles, you must use the ZSO format. However, out of the box, real consoles do not know how to read compressed files. You will need to ensure your console is running modern custom firmware.
To play .zso files on a real PSP or PSP Go, you need to be running ARK-4 or ARK-5 Custom Firmware (CFW).
Older legacy firmwares like PRO-C or ME do not support ZSO natively because the LZ4 decompression engine did not exist when they were created.
The developers of ARK completely rebuilt the PSP's disc driver (called Inferno V2) specifically to support .zso natively.
How to play: If your PSP is running ARK, simply drop the .zso files straight into your ISO folder on your Memory Stick, and they will boot flawlessly without the lag spikes associated with older CSO files.
To play .zso files on a real PS2, you must use Open PS2 Loader (OPL).
Note: You must be running OPL v1.2.0 Beta or newer, as stable 1.1.0 builds do not have ZSO support built-in.
The PS2 console only has ancient USB 1.1 ports, which are incredibly slow. If you try to play a standard, uncompressed .iso off a USB stick, the game's video cutscenes (FMVs) will often stutter or lag because the USB port cannot push the heavy data fast enough into the console's RAM.
Because .zso files are highly compressed, less physical data has to travel through that slow USB port. The PS2's CPU is surprisingly powerful, and it can unzip the LZ4 data much faster than the USB port can transfer uncompressed data.
This means that using .zso off a USB stick can actually cure video stuttering and significantly speed up your loading times!
No, do not compress PS3 games to CHD or CSO! Unlike PCSX2 (which adopted CHD) or Dolphin (which adopted RVZ), the RPCS3 development team has not officially adopted any compressed disc format. RPCS3 strictly does not support the CHD format. If you compress your PS3 ISOs into CHD, the emulator will completely fail to read them.
How to save space on PS3 games:
-
Scrubbing: Ripped PS3 games often contain gigabytes of useless dummy data and old firmware updates (the
PS3_UPDATEfolder). You can use community tools like PS3 ISO Tools to safely "scrub" (delete) this junk data from the ISO while keeping it 100% playable. - OS Compression: You can use "transparent OS compression" (like CompactGUI on Windows 10/11 or APFS compression on Mac). This forces your computer's hard drive to shrink the folder, but tricks RPCS3 into thinking it is totally uncompressed.
Native PS Vita games (like Persona 4 Golden) do not have a playable compressed format.
Unlike the PSP, the Vita does not use .iso files for its own games. Instead, native Vita games are simply installed as a standard, uncompressed folder structure on your memory card (usually via the NoNpDrm plugin).
(Note: If you are using Adrenaline on your Vita to play PSP or PS1 games, Adrenaline acts exactly like a real PSP. You absolutely CAN use CSO, ZSO, and CHD files inside Adrenaline!)
If you used a very early version of the TUI, Option [6] Auto-Update CLI Tool may have printed "Success!" without actually updating the tool.
Because the auto-updater relies on sudo (your Mac/Linux admin password) to move the newly downloaded file into your system's global /usr/local/bin folder, running the installation script instantly through a piped stream (curl | bash) caused the OS to block the password prompt from showing up.
The Fix: This has been permanently patched in v1.4.0+. To fix a broken installation, simply run the master installation command directly in your terminal one last time:
curl -sL https://github.com/wako69420/iso-compressor/releases/latest/download/install_mac.sh | bash