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→CHD Compression
==Applicable to All Platforms==
===Audio-CD===
Sega-CD, PC-Engine, PlayStation, Sega Saturn... what do these all have in common? They all use a regular CD format! Game developers often stored music and other sounds using the Audio-CD format, but it was terribly inefficient when it comes to disc storage as it also had to store the actual game along with the sound files. To put it in perspective, a 700 MB CD containing nothing but Audio-CD data can hold at most around 80 minutes worth of sound data, meaning games that used a lot of sounds where were limited in size.
Since then developers no longer use Audio-CD format and instead prefer custom audio formats that come included in the "game data" part of the disc. By the time the PS1 generation came, the Audio-CD part was just used for messages like "Don't put this in a CD player!" and little else (exceptions exist, of course!)
'''Instructions'''
Place chdman.exe and extractcd in the same directory as the dumps you want to compress (dumps must be in BIN+CUE format). Open Command Prompt and navigate to the directory where you placed chdman.exe and input one of the following:
* BIN/CUE to CHD: <code>for /R %i in (*.cue) do chdman createcd -i "%i" -o "%~ni.chd"</code> (Windows)* CHD to BIN/CUE: <code>for /R %i in (*.chd) do chdman extractcd -i "%i" -o "%~ni.cue"</code> (Windows)
Alternatively, if you only need to do one file you can use this: <code>chdman createcd -i "<FILENAME>.cue" -o "<FILENAME>.chd"</code>
* '''Can be reverted?''' Yes, using the same tool (chdman).
* '''Playable on Hardware?''' No.
* '''Playable on Emulators?''' libretro Beetle PSX, Avocado, DuckStation and PCSX ReARMed.
==PlayStation 2==
===GCZ (Dolphin native archive format) - GC/Wii===
Dolphin can't play games directly from compressed archives (7zip/zip/gzip/rar...). Instead, it utilizes its own compression method.'''This format has been deprecated in favor of [[#RVZ (Modern Dolphin format) - GC/Wii|RVZ]].'''
* '''Archive-quality dump?''' Not directly (can be restored with NKit).
* Zelda Twilight Princess (GC): 1.4 GB (original) > 1.4 GB (GCZ) (game data already fills the disk)
* Megaman Collection (GC): 1.4 GB (original) > 1.1 GB (GCZ) (sound data is stored as uncompressed stream to fill disk)
===RVZ (Modern Dolphin format) - GC/Wii===
The Dolphin team developed a new compression format based on WIA called RVZ. Unlike all the previous formats, RVZ is lossless and can preserve the padding data on Wii discs as well as the necessary files needed by the Wii's IOS. Usage is very similar to GCZ in Dolphin itself, but it only works on newer Dolphin versions.
* '''Archive-quality dump?''' Yes.
* '''Gain:''' Immediate (ISO dump size lowers). Considerable, depending on the game.
* '''Tools Used:''' Dolphin 5.0-12188+ (right-click the game(s) in the games list and select "Compress ISO..." (or "Compressed selected ISOs..." if more than one is selected))
* '''Can be reverted?''' Yes.
* '''Playable on Hardware?''' No.
* '''Playable on Emulators?''' Only Dolphin.
===Scrubbing and Trimming - GC/Wii===
