Sony's PlayStation Classic mini console has only 20 preloaded games, and there is no built-in mechanism to add more. However, the system uses a popular open-source PlayStation emulator to execute its ROMs, making unofficial expansion more or less inevitable.
Just a week after the official release of the gadget, modders have ripped wide open software to boot PS1
The process is a bit fussy, but essentially it is running a single PC application and checking that files are properly stored and labeled. At the moment, changing the console's built-in memory is not that easy, but that's not practical anyway. PlayStation ROMs are much larger than those of NES and SNES, whose mini-editions were also hacked and expanded quickly.
But for all those players who are saddened by the exclusion of the one PlayStation title they have loved, there is now a documented process called Game on the Classic. More generous ROM support for other consoles may be available later, as the PlayStation Classic definitely has enough performance for 8- and 16-bit emulators. Gamers hoping to build a dedicated emulation box could be served by something like a Raspberry Pi or an NVIDIA SHIELD.
Source: GitHub via The Verge