A full PSP ISO is up to 1.8 GB, and PS2 ISOs are 4 GB or more. Compressing them to CSO or CHD often saves 30–60% of the space with no loss in quality: the emulator unpacks the data as the game runs. Here’s how to do it for free on a Windows PC.
CSO or CHD?
| Format | Best for | Size saved | Works in |
|---|---|---|---|
| CSO | PSP games | Good | PPSSPP (all versions), PCSX2-based PS2 emulators |
| CHD | PS2, PS1 and PSP games | Best | PPSSPP (recent versions), ARMSX2 / NetherSX2 / PCSX2, DuckStation, RetroArch cores |
For PSP, CSO is the safe choice that works everywhere. For PS2, use CHD.
ISO to CSO with maxcso (PSP)
- Download maxcso from its GitHub releases page (it’s free and open source) and unzip it into a folder.
- Put your ISO in the same folder.
- Drag the ISO onto
maxcso.exe. A.csofile appears next to it when it’s finished. - Alternatively, open a command prompt in that folder and run:
maxcso game.iso - Test the CSO in PPSSPP, then delete the ISO.
To compress many games at once, put them all in the folder and run maxcso *.iso.
ISO to CHD with chdman (PS2, PS1, PSP)
chdman is a small tool that comes with the free MAME emulator. Download MAME from its official site, and copy chdman.exe from the MAME folder into the folder with your games.
| Game | Command |
|---|---|
| PS2 DVD game (.iso) | chdman createdvd -i game.iso -o game.chd |
| PS2 or PS1 CD game (.cue + .bin) | chdman createcd -i game.cue -o game.chd |
| PSP game (.iso) | chdman createdvd -hs 2048 -i game.iso -o game.chd |
Open a command prompt in that folder (type cmd in the File Explorer address bar and press Enter), paste the command with your file name, and wait. Big PS2 games take a few minutes.
Make a text file called convert.bat next to chdman.exe with this line, then double-click it:
for %%i in (*.iso) do chdman createdvd -i "%%i" -o "%%~ni.chd"
Can I compress on my phone?
It’s possible with some Android apps, but it’s slow and drains the battery, especially for 4 GB PS2 games. A PC is much faster. Then copy the CSO or CHD files to your phone over USB.
Tips
- Keep one test before deleting. Open the compressed game and play a minute before you delete the ISO.
- Don’t zip compressed games. Zipping a CSO or CHD saves almost nothing.
- Very old phones may load CSO/CHD games slightly slower. On any phone from the last five years you won’t notice.
Next: add the games to PPSSPP or set up ARMSX2 for PS2 games.
FAQ
Does CSO reduce game quality?
No. CSO and CHD are lossless: the game data is exactly the same, just compressed. Only the file size changes.
Is CHD better than CSO?
CHD usually saves more space and is the best choice for PS2 and PS1. For PSP, CSO works in every PPSSPP version, while CHD needs a recent one.
Does ARMSX2 support CHD files?
Yes. ARMSX2 and other PCSX2-based emulators open CHD files, which are the recommended format for PS2 games.
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