The very first game to make use of the Saturn's cartridge slot.  SNK wanted to port their Neo Geo hit to the Saturn as an arcade prefect port.  This wasn't possible due to the limited size of the Saturn's internal memory.  So what SNK did was to release the game on CD along with this pack in cartridge.  On the cartridge are all the files needed for character animations and so on.  How it worked was that the Saturn would load in the game's data from the CD and at the same time access the cartridge whist the game was running for all the animation frames needed.  After King Of Fighters '95 was released Sega made the 1 Mbit Ram cartridge then the 4 Mbit Ram cartridge.  These work in a similar way to the SNK cartridge except that those carts could be used by any game since all they had to do was load up the information needed for animation and store it on the cartridge.  The SNK KOF '95 cartridge however is read only making it only work with KOF '95,