The SNES CD BIOS ROM dump of the cartridge that came with the Super Famicom Play Station unit found by Terry and Dan Diebold. The ROM was dumped using a Game Doctor and released in 2016/03/01. Also officially named "Super Disc System Cartridge".

This cartridge would have been used to play Sony SNES CD games. Contains a bunch of BIOS functions in the ROM, alongside 256KB of WRAM (S-WRAM chips) and 8KB of battery backed RAM for saves.

A monitor debug menu can be accessed by pressing A + X at the main screen.

These strings can be found inside the ROM:

Super Disc boot ROM ver.0.95 Jul. 14, 1992 by Tomomi Abe at SONY

Super Disc BIOS program ver.0.93 by Tomomi Abe. May. 26 1992 at SONY.

Download Super Disc System Cartridge (Japan) (Prototype)

The Cutting Room Floor's page (contains more information and translations)

Screenshots

Main Screen Monitor Menu Self-Check 1 Self-Check 2 ADPCM Communication CXD-1800 BACKUP RAM