Love them or loathe them, flash cartridges are here to stay. From their early origins as a basic means of loading up ROMs on authentic hardware, we've seen these often misunderstood products grow in both scope and stature – and Terraonion's Mega SD could perhaps be considered the zenith of the concept.

On the surface, it may look like any other flash cart you've seen (although it's based on the Virtua Racing cartridge shell, rather than the standard one), but in reality, the Mega SD is a lot more interesting – because it's not just giving you a means of playing ROMs on your dusty old Mega Drive / Genesis, but actually replicates the performance of a Mega CD via FPGA technology. Who needs the Mega Drive Mini, right?

Now, this isn't the first time that Terraonion has performed this 'optical disc emulation' party trick; it's the company responsible for the Super SD System 3 expansion module, which bolts onto the back of a PC Engine / TurboGrafx-16 system and plays CD-ROM titles. However, while the premise (and the tech) is very much the same, the Mega SD feels that little bit more impressive due to the fact that the Mega CD itself was more than a simple means of adding storage space and improved audio; it boasted its own Motorola 68000 CPU (clocked 5 MHz faster than the one inside the Mega Drive itself), 6 MBit of RAM, was capable of displaying crude FMV and could scale and rotate both sprites and backgrounds – something that gave it a degree of parity with the Mode 7-packing SNES. In short, it was a much more robust enhancement to the base system, and the fact that Terraonion has managed to replicate it on a hardware level is remarkable (well, it certainly feels that way if you're old enough to remember how futuristic the Mega CD felt back in the early '90s).

The Mega SD has a pretty slick UI, especially when compared to other flash carts on the market. You can tinker with a wide range of settings and load both ROMs and CD images with ease – these are stored on a Micro SD card which slots into the side of the cartridge itself. You'll need to supply a BIOS file to run CD titles (and the BIOS has to match the region of the game you're booting up) and it's possible to assign multiple BIOS files to cover each territory.

Pushing up and start on your pad, you can summon an in-game menu which allows you to return to the Mega SD's main menu, enable cheat codes and save (or load) states; a whopping eight different save slots are available. The Mega SD simulates what a real-world Mega CD system would do when it comes to internal storage; it has both internal memory (which was included on the Mega CD via a battery back-up save system) and the option to save to a 'virtual' RAM cartridge. These, in reality, were cartridges that plugged into the Mega Drive's cartridge slot and gave players additional storage space (for some titles, like Shining Force CD, owning one of these was a requirement as progress from the game's opening chapters could only be carried over by using the backup RAM cart as the internal memory wasn't large enough).

The Mega SD is so clever that it even allows for disc-swapping – a process that was required for some of the larger Mega CD releases, like Night Trap, which recently saw release on Switch. A hardware button on the side of the cartridge allows you to swap discs (assuming the files are in the correct place on the SD card) but if you're too lazy to get up from your seat, the process can be done via the 'up + start' in-game menu as well.

Given that CD games in the '90s were fighting against the constraints of the hardware and memory standards of that period, it's no surprise that many Mega CD games exhibit lengthy load times as the data is spooled from the single-speed drive to the console's RAM. The Mega SD, being a solid-state device, isn't subject to these limitations and as a result, drastically speeds up the loading time on many titles. There are, however, some games which are programmed to factor in 'seek' times from a real disc, and removing load times would actually result in audio being out of sync with the visuals (usually during cutscenes). Thankfully, the Mega CD's firmware actually has a list of titles which do this, so you shouldn't notice any issues, assuming you keep the cart's firmware up to date.

While support for Mega CD titles is the headline feature here, it's worth noting that – as well as playing Mega Drive titles (including Virtua Racing, which has proven to be a no-go for previous flash carts due to the inclusion of Sega's custom SVP chip) – you can also play Sega Master System games on this device, as well as leverage the improved FM sound module that was only released in Japan. Sadly, save state support is not possible when playing these 8-bit releases, and support for Master System is limited to those models of the Mega Drive which come with the Master System hardware built-in; certain revisions (including the portable Nomad) lack this and therefore will not play Master System ROMs without internal modification. 32X games can also be loaded via the Mega SD, but you'll need the 32X module itself in order to do so – and, like with the Master System, there's no support for in-game save states. In fact, with the Mega SD connected to your base console via the 32X, you cannot load Mega CD or Master System ROMs – this is down to the way in which the two pieces of hardware 'talk' to one another. That means the few 32X CD-ROM titles available will not work on this device, but that's no massive loss as they're nothing to write home about.

Oh, and while we're here, it's also worth noting that the Mega SD will not function if your Mega Drive is already connected to a Mega CD, as this causes some kind of hardware-level confusion to occur. This might not sound like a big problem – especially if you're buying one of these cartridges to either avoid investing in a (now quite collectable and expensive) Mega CD unit, or to replace a unit that has failed – but it has serious ramifications for those lucky enough to own either a JVC Wondermega or Sega Multi-Mega / CDX. As these systems are all-in-one variants which fuse the Mega Drive and Mega CD together, you can only boot Mega Drive and Master System ROMs on them via the Mega SD.

One of the coolest features included on the Mega SD is what Terronion is calling "Mega Drive Plus" titles. Those of you who regularly read Nintendo Life will be aware that there's a trend for updating SNES titles with CD-quality audio tracks which can be loaded up either via emulation or using a flash cart with the correct tech inside. Mega Drive Plus is essentially the same thing; the game ROM is loaded as normal but the music is CD-quality stuff, which is naturally a big improvement over the Mega Drive's built-in audio. The catch here is that there aren't many of these specially-modified titles available as yet, but the stunning version of Streets of Rage 2 – complete with a reimagined variant of Yuzo Koshiro's sublime soundtrack – shows how much potential there is for future releases.

It's worth touching a little more on compatibility here. The unit works fine on original Sega hardware, and will even run on a Nomad (although an internal mod is required to ensure that you get CD audio). Clones are more hit-and-miss; the unit refused to work on our Columbus Circle 16Bit Pocket MD, and if you own any other variant, you might want to check online before ordering. Perhaps the best platform to use the cart with is the Analogue Mega Sg, which delivers amazing visual clarity and a whole host of other features.

System Mega CD

Sega CD Mega Drive

Genesis 32X Master

System Mega Drive

Genesis

(Model 1 or 2) Yes Yes No

(requires 32X unit) Yes Nomad Yes

(needs mod for audio) Yes No Yes (needs mod) Genesis 3 Yes

(needs mod for audio) Yes Untested Untested Mega Drive

+ Mega CD Requires Mega CD to be removed Yes No

(requires 32X unit) Yes Mega Drive

+ 32X No

(Requires Mega CD to be removed) Yes

(no region patch available) Yes No (32X must be removed) Mega Drive + Mega CD

+ 32X No

(Requires Mega CD to be removed) Yes

(no region patch available) Yes No (32X must be removed) Mega Drive

+ 32X

+ MSDEXP adapter Yes No

(requires Mega SD to be in cart port) Yes (and 32X CD games) No

(requires Mega SD to be in cart port) Multi-Mega / CDX No Yes No

(requires 32X unit) Yes Multi-Mega / CDX + 32X No Yes Yes No (32X must be removed) Analogue Mega Sg Yes Yes No Yes Columbus Circle 16Bit Pocket MD No No No No

All in all, the Mega SD is a remarkable feat of engineering; it takes a bulky optical drive and condenses it into a sleek and elegant cartridge, opening up the Mega CD library without the need to drop untold amounts of cash into picking up titles like Shining Force CD, Snatcher and Lunar on the secondary market.

It also overcomes the issue of failing Mega CD units; disc-based systems aren't as resilient as cartridge-based ones, and it's a matter of when – not if – your own system gives up the ghost. The counterpoint here is that the Mega SD is quite expensive, retailing for €232.00. Now, if you add up the cost of a Mega CD unit and a handful of the best games for the format, you'll blast past that figure effortlessly – but in an age where many people are content with emulating such systems on their smartphone, this is clearly a product aimed at a very specific sector of the market – and that sector will absolutely love it to pieces.

Thanks to Terraonion for supplying the unit used in this review.

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