Sufami Turbo

The Sufami Turbo is a 1996 Bandai adapter that goes into a Super Famicom’s cartridge slot and takes two small cartridges of its own. It is the only unit in RetroXR with more than one bay, and the reason a bay is addressed by number at all.

The adapter in the console's slot with both wells filled. The Super Famicom wears the procedural stand-in — it has no modelled shell yet — and the cartridges are unlabelled here.

Two slots, and why they matter

The second slot is not a spare. Nine of the thirteen Sufami Turbo games link the cartridge in slot B into the game in slot A: the six SD Gundam Generation titles lend each other their units, and SD Ultra Battle lends its characters across the pair. A one-slot Sufami Turbo would be the wrong machine rather than a simplified one.

Put the adapter into the Super Famicom’s slot, then drop a cartridge into each well. One cartridge on its own is a first-class configuration, not half a pair — the core sniffs the first cartridge and maps slot B empty. Poi Poi Ninja World runs that way.

See expansion hardware for how a stack is assembled.

What you need

• STBIOS.bin in libretro/system/snes9x/ — the adapter’s own shell program. Until it is installed, the Sufami Turbo is not offered in the spawn menu at all.
• snes9x, which RetroXR selects for you when the adapter goes in.
• Your cartridge dumps in the sufami_turbo folder of your ROM library.

Without the BIOS it does not quietly degrade — it refuses

A missing STBIOS.bin does not fall back to loading the cartridge as an ordinary Super Famicom game. The load is refused outright: zero frames, and a content-load failure. The spawn gate is there so you meet that as a missing file rather than as a black screen.

Your dumps are named .sfc, not .st

Every Sufami Turbo dump in circulation carries the .sfc extension, the same as an ordinary Super Famicom game. RetroXR therefore accepts both .st and .sfc under this system — otherwise your cartridges would be filed under Super Nintendo and the adapter’s bays would refuse them.

Keep them in their own folder

Because the extension does not distinguish them, what separates a Sufami Turbo cartridge from a Super Famicom game here is which folder it is in. Put the small cartridges in roms/sufami_turbo/.

Both cartridges keep their saves

The adapter has no battery — the cartridges do — so each one saves independently, and RetroXR gives slot B a save file of its own.

That took a fix. snes9x reports slot A’s save RAM and the plain save RAM from the same place, while slot B sits behind a core-specific memory id of its own. Reading only the obvious one gave the same 16 KB whether one cartridge was in or two, so a linked pair kept only half its progress — SD Ultra Battle said as much on every launch, reporting that the B cassette’s backup was not initialised.

A save is keyed to the cartridge, not to the slot it sits in, so a game carries its save between the two wells, and lending it to a different pairing does not overwrite what is on it.

Verified with

Measured 2026-08-30 against the No-Intro set: SD Ultra Battle: Ultraman Densetsu in slot A with Seven Densetsu in slot B, running 767 frames at 256×224 — with the game itself reporting the B cassette’s backup state, which is the proof the link is live. A game that could not see slot B would have nothing to say about it.