There are a few different file formats that you will find relating to the GameBoy which are listed below:
- .ISX Official Nintendo ROM file (compiled by the assembler ISAS) (contains debug symbols)
- .GB Original GameBoy ROM file (no debug symbols) the exact contents of the ROM chip inside the cartridge
- .GBC Original GameBoy Color ROM file (no debug symbols) the exact contents of the ROM chip inside the cartridge
If you backup your own games they will be created with a .GB or .GBC file extension along with most of the ROMS that can be found online. If the ROM was leaked from a first party developer such as Nintendo then they will likely be in .ISX format, this can easily be converted to .GBC with the tool CVTISX included in the Official GameBoy SDK.
The emulator SameBoy recently added support to play ISX files due to the 2020 Nintendo Leaks:
This SDK seems to use a number of different file formats, but it is not clear what exactly is the purpose of each.
In the Nintendo Gigaleak we found that the following file formats were used to store source code:
- .DMG - Assembly source code for the Dot Matrix Game (Game Boy)
- .X65 - Either Famicom or Super Famicom source code
- .S - Game Boy Color assembly source code
- .CVT - Custom Conversion scripts that can be executed with FCV
- .COM - Compiled Game Boy ROM file, unsure difference between this and ISX
- .O - Assembled output of a .DMG/.S/.X65 Source code file
- .HEX - Plain data file for including in the ROM - could be anything
- .BIN - Binary file for including in the ROM - could be anything
We know the following file formats are related to Graphics on the Game Boy (Color) but we are not sure tghe exact purpose of all of them (most were seen in Zedla DX source code):
- .CHR - Character Graphics Data from Famicom and Game Boy (2 bits per pixel planar)
- .CGX - Seems to be exactly the same as .CHR (2 bits per pixel planar)
- .CGE - Character Graphics data (For famicom?)
- .DCG - Character Graphics data (for DMG Game Boy?)
- .CCD - ?
- .CSD - Possibly compiled to .CGX
- .CDT - Color Data Table? (related to CSD)
- .COL - Color pallete? (Related to CDT)
Most of these have been seen in the Zelda DX Gigaleak but we are unclear what exactly they are.
- .SCR - Screen file maybe containing location of character tiles in a level?
- .ICE - Something to do with the In-Circuit-Emulator?
- .MDT - Map Data Table? (Something to do with Game Maps)
- .PDT - Pattern Data Table?
- .PNL - Pattern Number L ? (Has file header: NAK1989 S-CG-CAD Ver 1.23)
