You will rarely find ECM alone anymore. It was a method to undo the error correction data on CDs. Most "hot" packs now convert ECM to CHD.

Verdict: If you see a file ending in .chd or .pbp, you have found a "highly compressed" gold mine.

Pro Tip: Use a tool called NamDHC (PSX Compression Suite) to verify if a ROM is truly "hot" compressed. It will show you the original LZMA ratio.

If you are searching for "hot" ROMs, you will encounter three file extensions. Here is what they are and which one you want.

For the average player, a PlayStation 1 game is a CD-ROM—audio tracks, high-resolution (for 1994) prerendered backgrounds, full-motion video (FMV), and orchestral or redbook audio. For the high-compression enthusiast, most of that is "bloat." Their lifestyle is defined by minimalism: the belief that gameplay mechanics, level geometry, and core logic can survive while everything else is stripped, downsampled, or re-encoded to the threshold of acceptability.

This lifestyle emerged from necessity—slow dial-up connections (a 700MB download in 2002 could take days), tiny hard drives (6-10GB was common), and the rise of portable devices like the PSP, early Android phones, and low-power handheld emulators. Today, it persists as a form of digital asceticism. Why carry a 2TB SSD with 200 games when you can fit 800 highly compressed games on a 32GB microSD card?

This is the minefield. Searching for "PSX Highly Compressed ROMs hot" on Google will return hundreds of sketchy "ROMs generator" sites. Here is where the actual scene hangs out.

Use RetroArch with the "SwanStation" core. RetroArch loves CHD files. It will treat your compressed library as if they were native cartridges.

Not all emulators can read highly compressed CHD or PBP files. Here is the current "hot" setup: