You'll see a list of all the systems supported by Mednafen (as shown toward the right). If Mednafen is already open, close it and re-open it after you've plugged in the gamepad. If you want to configure a gamepad, plug it in now.Unlike other Mednafen frontends before Mednaffe, Mednaffe allows you to easily configure the all keys for every system in advance! This saves you a lot of trouble. You get a ROM image is too large error.Or just use uoYabause or SSF instead, because they'll run any Saturn ISO. The best thing to remedy this is to download the game from another website and cross your fingers and hope it'll work with Mednafen.
So my directions in loading a game apply the same way:
*If your Saturn game is currently in a ZIP, 7Z, or RAR file, it must be extracted. Place the BIOS files in Mednafen's main directory, as shown here.sega_101.bin - required for Japan-region games.
Hence, proceed with the following directions anticipating that your Saturn ISO may get rejected. People will tell you “ Oh, well it's not working because you downloaded a bad ISO.” Yet your 'bad ISO' works fine on uoYabause and SSF. It especially likes to reject fan translated games. There's maybe a 50/50 chance that Mednafen will reject your Saturn ISO. While Mednafen can emulate Sega Saturn games well (uoYabause actually does it better), Mednafen is plagued with poor ISO compatibility (not to be confused with game specific compatibility). And if you haven't already, you should read Setting up the keyboard or gamepad so you can actually play the game.
Anyway, here's how to load PlayStation 1 games with Mednafen: