Executeables, "Program Files":
------------------------------

GXB*,AXF,BIN     Arm eXecutable Format: binary executable which starts with a
                 branch and 6 address fields

                 This is placed in gp32 ram starting at location 0xc000000. The
                 entry point is the starting location and the entry is
                 performed in ARM (not thumb) mode. Here is the header format:

                            b SkipHeader
                            DCD Start Of Rom Code       @ (?)
                            DCD End Of Rom Code         @ (?)
                            DCD Start Of BSS Section    @ (?)
                            DCD End Of RAM Sections     @ (?)
                            DCD Start Of DATA Section   @ (?)
                            DCD End Of RAM Sections     @ (?)
                            DCD 0x44450011
                            @ ... sometimes more info here...
                 SkipHeader:
                            b EntryPoint

   GXE           Gamepark eXecutable Encryption info: contains name, icon,
                 encryption info.
   GXC           Gamepark eXecutable Contents: contains the remaining part of
                 the executable data.

                 Usually only the first X bytes of a commercial gxc is
                 encrypted. The percentage of the file that is encrypted is
                 controlled by the encryption program. (But often it is a very
                 low percentage.) Here is the format

                 Header (20 bytes long)
                 Encypted binary data (X% of file)
                 Unencrypted binary data (100-X% of file)

                 If you remove the 20 byte header and unencrypt the file, then
                 the resulting data is identical in all other respects with a
                 .gxb file.

   GXF           Gamepark eXecutable Free/Format: plain executable with icon/
                 application info
                 [file header chunk]
                    0 -  3  : File ID. "gxf " (4byte)
                    4 -  7  : file size - 8 (4byte)
                 [info header chunk]
                    8 - 11  : info Header Size - (4byte)
                   12 - 12  : icon image flag (if 1, the icon image exists.) (1byte)
                   13 - 13  : the length of application program title= t_len (1byte)
                   14 - 13 + t_len : application program title(t_len byte)
                   14 + t_len -  13 + t_len + 256 : icon image data (256 byte)
                 [data chunk]
                  270 + t_len - 273 + t_len       : axf (ARM excutable file) data size (4byte)
                  274 + t_len -                   : axf data (plain binary)

   FXE           Scrambled (light encryption) binary file & graphic icon for
                 free games/apps from GP & third party developers. You have to
                 use Game Park's free launcher to run these on your gp32. When
                 the launcher unscrambles these files and removes the icon, the
                 result is identical to a .gxb file. They are usually found in
                 the gp:\GPMM directory.

Resource Files:
---------------

   GPG          Graphic File
                0 - 3   : File ID. "gpg " (4byte)
                4 - 7   : Date size = file size - 8 (4byte)
                8 -     : Data

   SEF          PCM File
                0 - 3   : File ID. "sef " (4byte)
                4 - 7   : Data size = file size - 8 (4byte)
                8 -     : Data

   GFT          Font File
                0 - 3   : File ID. "gft " (4byte)
                4 - 7   : Data size = file size - 8 (4byte)
                8 -     : Data

Distribution Archives:
----------------------

   ZPK           ZPacKed archive: contains directory structure of an encrypted
                 application
   FPK           Free zPacKed archive: contains directory structure of a free
                 application
   GPK           unencrypted zPacK archive

   SMC,GP*       SmartMedia Card memory dump file

Security:
---------

   GPS           GamePark uSer: contains the username, password, GP32 ID (all
                 in encrypted format)
   GPM*          GamePark Media: contains the gamename (not defined), size (not
                 defined), SMC ID

  *) not official

[info shamelessly copied from darkfader's site and some other source i dont
 remember.]