The sega saturn was the second released Sega console which used CD-ROM to distribute its games, one of the benefits of the CD-ROM format is many times more space than a cartridge. One of the downsides compred to cartridges however was the slower loading times as reading from a CD is much slower than reading from a ROM chip.
Unlike most cartridge based ROM chips CDs have a standard File System to read files from and so instead of everything being in a giant blob of binary and burned to a chip, the game could be split into multiple files.
Also the consoles would not have enough RAM to hold all the game assets so games would have to stream assets into memory when needed. So it would only read the texture or sound files used in a particular level and ignore the rest.
This makes it slightly easier to do some basic modding of Saturn assets compared to a ROM based console such as the Mega Drive, as you can normally pinpoint the asset you want down to a particular file and sometimes they have file extensions that tell you exactly what format the file is.
Sega Saturn Executables are actually COF/COFF (Common Object File Format) files which is a precursor to the ELF executable format that is used on most future console platforms.
ABS files seem to be the output of the LNK command and are specified in
.lnk makefiles. Each sample in the SDK builds an ABS file along with the COFF executable. They both seem to be a collection of object libraries (assembled code) but not sure the difference between the formats.
Sometimes these are listed as “Execution files” so I am not sure if cof is the default executable format or not anymore.
ABS Files are listed in the documentation as “Absolute load module file “
Many Sega Saturn CD-ROM games use this file format to store frames of a Cinepak-compressed video interleaved with uncompressed PCM audio. When this is the case, the files will typically have the extension .CPK (which is why FILM files are usually known as CPK files). Sometimes, audio-only FILM files will have a .SND extension.
A quick look at the PCS File format from the Sega Saturn game Exhumed/Powerslave:
Virtual Disc image used by developers when using the Mirage CD Emulator.