CD-ROM and DVD-ROM based rom files can be a bit confusing. When CD-ROM burners first became publicly available, many different companies made their own software for ripping and burning disks, and there were many proprietary formats created for storing that data. Because of that, there is no set standard for storing CD or DVD-ROM info. While the emulation community has settled on a few common formats, they aren’t always the same between different software catalogers (e.g. no-intro, TOSEC), and sometimes are different across game systems in even a single catalog.
There are currently two types of ROM storage formats: compressed and uncompressed. Compressed ROMs offer two advantages: they require only one file to represent a disk, and they take up less hard drive space. Uncompressed roms tend to require at least two files, sometimes more, because they separate out data and track listings.
MAME is currently leading a push to standardize around the .chd (Compressed Hunks of Data) format, and that’s the format that we recommend for all CD and DVD based roms. If you have roms in other formats, you can convert them to chd.
The most common compressed rom formats you’ll run across are .chd and .pbp. We recommend .chd for all systems that support it. .pbp is an official format used by Sony for the PSP, so some PSP games will be in that format natively, but for other systems it can cause problems with achievements and lossy audio.
CHD is compressed format championed by MAME. It has very good lossless compression, and allows you to store games in a format where one file contains everything you need for one disk.
Roms are converted to chd format using the chdman command line program. The most recent version of it comes with each release of MAME. If you don’t feel comfortable with command line applications, there is also namDHC, a Windows frontend for chdman. You’ll still need to download MAME and put the chdman.exe into the same directory as namDHC.exe in order to run it.
There are many uncompressed rom formats, but the most common that you’ll encounter are .cue+.bin and .ccd+.img. These formats were created to give a CD burner instructions for how to write the tracks onto the CD. Because of this, these roms are usually split into a track listing (e.g. .cue, .ccd, .toc) and one or more data files (e.g. .bin, .img). There are a few formats, such as .iso, that don’t require a separate track listing.
While it’s possible to run a .bin file without a .cue file (or a .img without a .ccd file), these roms are incomplete, and you may have issues running the game. The most likely issue is that some of the game’s music will be missing. If you do have a .bin file that dosen’t have a .cue file, it’s recommended that you source a different rom file, as it’s possible the rom could be broken in other ways as well. If you don’t want to or can’t though, you can create a .cue file for your .bin using Duckstation’s Cue Maker.
AmberELEC also supports .m3u files for many systems. These files are playlists that contain a list of disk images. Using .m3u files, you can make it so that multidisk games only have one entry in your game list.
.m3u files are a plaintext playlist. They simply contain a list of all disks for a game. For example, if you have Final Fantasy VII in .cue+.bin format, an m3u will look something like this:
Final Fantasy VII [US] (Disk 1).cue
Final Fantasy VII [US] (Disk 2).cue
Final Fantasy VII [US] (Disk 3).cue
The entries in the m3u file should match the file names for your game. For any format that requires a .cue file, the m3u should list the .cue files. For roms in other formats, such as .chd, the file would list the .chd files instead.
AmberELEC has an automatic m3u generator for PlayStation in the Tools section called PSX - Create m3u files. Depending on how your files are named, you may need to adjust the m3u files it creates.
You can create m3u files for single disk games as well, and the m3u generator will generate m3u files for those games too. Having an m3u file for all your games means that you can hide all the other extensions (.cue, .chd, etc.) and have a clean list of games. If you don’t want to do this but still want to use m3u files for your multidisk games, you can hide the disks individually so that only the m3u shows in your games list.