Can SNES play NES games? That question is older than the SNES itself. But the two systems aren’t backward compatible, unfortunately. There are modern options that are, however. More on that in a minute.
There are physical limitations that prevent an NES cartridge from even fitting in an SNES. But there was a technical reason to make the two physically incompatible. Even if the cartridge would fit, it wouldn’t work.
Differences between the NES and SNES
Nintendo could have, in theory, made the Super Nintendo backward compatible with the NES so it could run NES video games. Both consoles used variants of the venerable MOS 6502 processor, so the two systems’ CPUs at least spoke the same language. But Nintendo didn’t make the audio and video chips in the SNES backward compatible with their NES counterparts.
Of course, this may sound a lot like the difference between your old PC and your new one. Same CPU family, just a faster version in the new one, and new audio and video chips. No big deal. Device drivers take care of everything, so you can just load your old games and go.
That’s part of the difference between modern gaming and retro gaming. When your CPUs run at 3 GHz, you just abstract away the hardware, use device drivers for everything, and your software doesn’t have to worry about the differences in the chips. When your CPUs run at 3 megahertz, there aren’t enough cycles for all that overhead. You either build the new hardware around and on top of the old hardware so everything’s where the game cartridges for the old system expect it, or you scrap backward compatibility and start over.
Why Nintendo didn’t make the NES and SNES compatible
Nintendo had a couple of options when it came to compatibility. They could have designed the audio and video chips to be compatible from the start. This would have increased their cost and complexity and slowed down the time to market. It may have also limited the capability. The whole point behind 16-bit systems was to have richer graphics and sound, to make Super Mario World an experience more like Sonic the Hedgehog than its 8-bit predecesssors.
Or Nintendo could have taken some sort of a dual route, placing two sets of chips in the console, one that was active when playing NES games, and another that was active when playing SNES games. This would have perhaps reduced complexity, but still would have increased cost.
Nintendo was rather late to market with the SNES. Sega and NEC both released 16-bit consoles nearly two years before Nintendo did, and Nintendo was happy just to ride NES sales. When the 16-bit consoles caught on, it kind of caught Nintendo by surprise. Nintendo needed to get the console to market, and meet a price point that would look reasonable. Had Nintendo started developing the system a couple of years earlier, they could have made a backward-compatible system, similar to what Apple did with the Apple IIgs, which could run Apple IIe software.
Why not an add-in?
Arguably, Nintendo could have developed an add-on module to plug into the SNES to essentially turn it into an NES. Nintendo did similar add-ins for Gameboy compatibility. The problem with this was that the NES’ sound was integrated into its CPU. Nintendo would have had to develop a discrete sound chip that would be compatible, or get someone else to develop it, in order to make the module feasible.
Nintendo executives probably figured anyone who wanted to play NES games would just hang on to their old NES console and play their old games on it.
What about newer systems like the Retron or FC Twin?
There are modern Nintendo-compatible consoles, such as the Retron 2, that can run SNES games and older NES titles as well. These can work one of two ways.
Any retro 8- or 16-bit system can easily be reimplemented today on a single chip, known as a system-on-a-chip, or SoC. These SoCs are fairly inexpensive today. A designer can simply place two or more SoCs on a motherboard, hook them up to compatible cartridge slots, and essentially cram multiple consoles onto a single circuit board that fits in an enclosure no larger than any one of the original consoles was.
These systems aren’t quite 100% compatible with the originals but they run most titles for both systems while being inexpensive and convenient.
A second option is to simply put a powerful enough CPU in the console to emulate the older console. This is the approach Nintendo takes with the NES Classic and SNES Classic and that hobbyists take with Retropie. Any SoC suitable for powering a low-end tablet or cell phone is fast enough to emulate the NES and SNES. Simply load emulator software onto it, place compatible cartridge ports on the board, and go to town. The Retron 5 is a console that takes the emulation approach. It’s compatible with NES, SNES and several other systems, and notably has HDMI output so it’s super easy to connect to an HDTV.
These options make it possible to make small, convenient retro consoles that can play NES, SNES, and even Sega Genesis cartridges with a single unit. But the options to do that today didn’t exist in 1990, so that’s why Nintendo didn’t do it then, and that’s why SNES can’t play NES games.