Reference Disc Images

CD- and disc-based systems don't use a single ROM file — they use a disc image, and some games span multiple discs. This trips people up more than anything else in emulation, so here's how the formats work and how to handle multi-disc games with an .m3u playlist. Applies to psx, saturn, dc, sega-cd, pc-engine-cd, and neo-geo-cd.

Disc image formats

Format	What it is	Use it?
.cue + .bin	A text .cue sheet that points at one or more .bin track files	Works everywhere, but a game can be several loose files
.chd	Compressed Hunks of Data — the whole disc (all tracks) in one compressed file	Preferred — smaller, tidy, widely supported
.iso	Raw single-track image (data only, no CD audio)	Fine for data-only discs; loses CD audio tracks
.gdi / .cdi	Dreamcast-specific images	Dreamcast only; .chd is the tidier alternative
.pbp	Packaged PS1 image (often multi-disc in one file)	PS1 only; convenient, DuckStation/PCSX read it

Load the descriptor, not the data track. For a .cue+.bin game you open the .cue, not the .bin — the .cue tells the emulator the track layout. Opening the .bin directly loses CD audio or fails outright.

Why .chd is worth it

A .chd packs every track of a disc — data and CD audio — into one compressed file, typically 30–60% smaller than the .bin set. One file per disc means nothing to lose track of, and every emulator on this wiki that plays discs reads .chd.

Convert with chdman (ships with MAME) on a PC:

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

Point it at the .cue (or .gdi for Dreamcast) and it pulls in the referenced tracks. To go back, chdman extractcd.

Multi-disc games and .m3u

Games like Final Fantasy VII (3 discs), Metal Gear Solid (2), or Grandia don't fit on one disc. If you load just disc 1, you'll have no way to swap when the game asks. The fix is an .m3u playlist: a plain text file listing each disc in order, which you load instead of an individual disc.

1. Put the discs in the game's folder, e.g. under sd:/roms/psx/Final Fantasy VII/:

   Final Fantasy VII (Disc 1).chd
   Final Fantasy VII (Disc 2).chd
   Final Fantasy VII (Disc 3).chd
   

2. Create Final Fantasy VII.m3u next to them containing one path per line:

   Final Fantasy VII (Disc 1).chd
   Final Fantasy VII (Disc 2).chd
   Final Fantasy VII (Disc 3).chd
   

   (Relative names work when the .m3u sits in the same folder.)
3. Load the .m3u. The emulator treats it as one game, and its in-menu disc-swap control moves between the listed discs — so saves and memory cards stay continuous across the swap.

This is the same idea across systems — Saturn, Sega CD, and PC Engine CD multi-disc games all use .m3u the same way.

Common mistakes

• Loading a .zip that wraps a disc image. Extract it first — disc emulators want the .cue/.chd/.gdi, not an archive of it. (Cartridge systems are the opposite: they read straight out of .zip.)
• Only downloading disc 1 of a multi-disc game and wondering why you can't finish it.
• Opening the .bin instead of the .cue.
• Missing BIOS — a disc system that boots to a black screen usually needs its BIOS, not a different image.