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Overview — CHD and PSX ROMs

CHD (Compressed Hunks of Data) is a container/compression format originally developed by the MAME project to store large disk- and tape-image data (CDs, laserdiscs, hard drives) more compactly while preserving exact, bit-for-bit data. CHD files can bundle CD-ROM images and related metadata (subchannel, TOC) needed to emulate optical-media-based games.

When people refer to “CHD PSX ROMs” they generally mean PlayStation (PS1) CD images stored in CHD format rather than standard BIN/CUE, ISO, or IMG formats. Using CHD for PSX images reduces file size and keeps multiple associated data pieces (subchannels, multiple tracks) together in one file.

CHD vs. Other PSX Formats

| Format | Size | Single File | Emulator Support | Lossless | |--------------|-----------|-------------|------------------|----------| | .bin/.cue | 100% | ❌ (often) | Universal | Yes | | .iso | ~95% | ✅ | Limited (no audio tracks) | No | | .pbp (PSP) | ~60-80% | ✅ | Many, but older | Yes | | .chd | 50-70%| ✅ | Growing, modern | Yes |

1. Massive Space Savings

A full PSX North American library (Redump set) occupies roughly 1.2 TB in .bin/.cue format. The same library in .chd fits on a 500 GB SSD. For handheld emulators (Steam Deck, Retroid Pocket, Anbernic devices), this is a game-changer. chd psx roms

Common formats and conversion

• Input formats: BIN/CUE (most common), ISO, IMG/CCD, NRG, and raw .sub/.toc setups.
• Tools:
  • chdman (part of MAME): primary official tool to create and manipulate CHD files. Usage examples:
    • Convert BIN/CUE to CHD:

      chdman createcd -i game.bin -o game.chd
      

    • Convert BIN/CUE with CUE:

      chdman createcd -i game.bin -cue game.cue -o game.chd
      

    • Extract CHD back to BIN:

      chdman extractcd -i game.chd -o game.bin
      

  • Some frontends and ROM managers integrate chdman for batch conversion.
• Recommended conversion settings:
  • Use lossless compression for preservation (default).
  • If storage is tight and audio size dominates, consider lossy compression for audio hunks with chdman options (careful: may affect audio fidelity).
  • Keep original CUE/TOC if possible so track layout is preserved.

How to Create CHD Files (Conversion)

You cannot simply rename a .bin file to .chd. You must convert your existing disc images using a tool developed by the MAME team.

Tools Required:

• chdman: A command-line tool included with MAME.

Step-by-Step Guide:

1. Download chdman: It is usually found inside the MAME binary package (extract the zip and find chdman.exe on Windows).

2. Prepare your files: Ensure you have your .cue file and corresponding .bin files in the same folder.

3. Open Command Prompt/Terminal: Navigate to the folder containing chdman and your roms. Overview — CHD and PSX ROMs CHD (Compressed

4. Run the command: Type the following command:

   chdman createcd -i "gamefilename.cue" -o "gamefilename.chd"
   

   • -i is the input (your existing CUE file).
   • -o is the output (the name you want for the new CHD file).

5. Wait: The process may take a few minutes depending on the size of the game.