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Sega CD

Sega CD icon Sega CD logo

Overview

The Sega CD (Mega CD outside North America) is the CD-ROM add-on for the Genesis/Mega Drive, introducing FMV, CD audio and larger sprites. REG-Linux treats it as the segacd system so that the appropriate themed artwork appears while allowing you to keep the files near your main Mega Drive/Genesis collection.

Technical specifications

  • CPU: Motorola 68000 clocked at 12.5 MHz with a dedicated co-processor for CD-ROM streaming.
  • Memory: 512 KB main RAM, 512 KB video RAM, 256 KB audio RAM, plus buffers for CD data.
  • Display: HuC6270-based video controller augmenting the HuC6280 core with overscan sprites and scaling for FMV.
  • Sound: 16-bit PCM plus Redbook audio streaming combined with the HuC6280 PSG channels.

Quick reference

  • ROM folder: /userdata/roms/segacd (legacy /userdata/roms/megacd remains valid)
  • Accepted formats: .cue, .iso, .chd, .m3u
  • Emulators: libretro: genesisplusgx, libretro: picodrive
  • System group: segacd, megadrive

BIOS

RetroArch cores expect at least one official Sega CD BIOS under /userdata/bios/.

MD5 checksum Filename Description
e66fa1dc5820d254611fdcdba0662372 bios/bios_CD_E.bin Europe BIOS
854b9150240a198070150e4566ae1290 bios/bios_CD_U.bin US BIOS
278a9397d192149e84e820ac621a8edd bios/bios_CD_J.bin Japan BIOS

Stay with the BIOS that matches your ROM region for best results.

ROMs

Place each disc image inside /userdata/roms/segacd. CHD archives are preferred because they pack the cue and track metadata together; .iso/.bin dumps should stay paired with their .cue. Use .m3u playlists to chain multi-disc releases or rely on the Quick Menu’s Disc Control to swap discs manually.

Emulators

RetroArch / GenesisPlusGX / Picodrive

RetroArch hosts both PicoDrive and GenesisPlusGX for Sega CD. Launch the Quick Menu ([HOTKEY] + south face button) to adjust shaders, audio latency, controller mapping, and per-game overrides. EmulationStation exposes:

  • megacd.videomode, megacd.ratio, megacd.smooth, megacd.shaders, megacd.pixel_perfect, megacd.decoration, megacd.game_translation
  • megacd.gfxbackend (OpenGL/Vulkan), megacd.audio_latency, megacd.video_threaded

GenesisPlusGX leans toward accuracy, while Picodrive favors performance on weaker SBCs. They both share options for sprite flicker removal, overscan cropping, and controller type selection per port.

global.pce_nospritelimit  – remove the 16-sprite-per-line cap
global.picodrive_cropoverscan – trim black borders
global.picodrive_controller1/2 – switch between 3- or 6-button pads

Controls

Use the Mega Drive overlay at ../images/controller-overlays/megadrive-1.png. It reflects the 6-button layout expected by most Sega CD titles, including the multi-button controller and optional light gun inputs.

Troubleshooting

  • Verify the BIOS and ROM region match—using a PAL BIOS with US discs can cause hangs.
  • Prefer CHD containers to avoid missing tracks on CDs with multiple sessions.
  • If a Lock-On cartridge fails, toggle the Lock-On option in the Quick Menu or use the patched Mega Drive ROM.
  • Consult the generic support pages for additional Sega CD guidance.