2GB of DOS Games (Doom, Heretic, Fire and Ice, Loom, Blood, Duke Nukem, ROTT, Strife, MDK, Jazz Jackrabbit, Alien Carnage, etc.)
600MB of GBA Games (Boktai, Metroid Zero Mission, Megaman Zero, Astro Boy, etc.)
512MB of Industrial Music (Feindflug, Funker Vogt, Fusspils 11, etc.)
200MB of Genesis Games (Sonic, Splatterhouse, Vectorman, Ristar, etc.)
5MB of GameGear Games (Tail's Adventure, Tail's Sky Patrol, Mean Bean Machine, etc.)
512MB of N64 Games (Conker's Bad Fur Day, LoZ Majora's Mask, Banjo Kazooie, Tonic Trouble, etc.)
256MB of SNES Games (Axelay, Front Mission, Metal Warriors, Demon's Crest, Earthbound, Illusion of Gaia, Lufia, Cybernator, Seiken Densetsu, etc.)
And the rest is for homebrew, and maybe some games that I have yet to discover (I have never tried MAME before, so maybe that will be interesting).