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The MegaSD is an all-in-one flash cart for the Sega Genesis / Megadrive that plays games from the Master System, Genesis, SegaCD, and 32X (with 32X hardware).

Firmware can be downloaded here Please note that you need to register your device. If firmware is not present after registering, your device was shipped with the most recent firmware already installed. (Current Firmware is 1.05 R07)

Manual is located here


  • Any storage size MicroSD card should work as long as it is FAT32 or ExFAT formatted. TerraOnion generally recommends avoiding Samsung branded cards as they have been known to cause issues on their devices. Sandisk is the preferred manufacturer.
  • CD games must be in their own folders. The folder name dictates the name that is displayed in the MegaSD menu for CD games. Nested folders are fully supported for both CD and cartridge games.
  • Sega CDX, Multi-Mega, X'Eye, Wondermega, Laseractive, etc. allow cartridge based games to load but CD games are disabled due to potential bus conflicts that could damage your original hardware.
  • If you have a SegaCD/MegaCD attached while using a MegaSD CD games are disabled (also to prevent a potential bus conflict).
  • Similarly CD games cannot run through a 32X. Using a MSDEXP from Mobius Strip Technologies can bypass this limitation and allow 32X CD games to work through the MegaSD.


  • Various hardware configurations can offer differing experiences. Please refer to our MegaSD Compatibility page.
  • Seek time emulation allows games to run at a simulation of the speed of an actual disc. If you have problems with a particular game try toggling it on and off. In most instances leaving it on works best. Also let the TerraOnion team know of your findings.

Game Compatibility & Known Issues

  • In-Game Menu and Save States do not work on Master System...yet


  • Blinking light - If the leds blinks, that means not enough power is reaching MegaSD. "There is a voltage supervisor in the cart, so if it drops below a threshold, it resets the board. I'd check for dirty contacts on the exp port, msdexp and megasd and see if there is some rust. It will create a higher resistance and won't allow full power to reach MegaSD." -Neodev

Tips & Tricks

  • MegaSD can use cfg files to alter the loading parameters for games. Details can be found on the Config File page.
  • Cover art, genre and release year info for ROMs can be added to the menu. Details can be found on the MegaSD Cover Art & Info page.