While FunKey S autosave save files (.quicksave) are entirely incompatible with external emulators, FunKey S emulator save state files (.000, .001, etc.) other than those of the PlayStation are compatible with matching emulators on other platforms, such as the PC version of FCEUX in the case of NES games. Additionally, for games that support them, the transfer of in-game saves is an alternative option that is generally compatible with a wider range of emulators. Note, however, that a third-party emulator having an in-game save file format with a matching file extension does not guarantee that it will be listed below, as other factors, such as expected save file size, can impact in-game save file format compatibility between emulators. As battery-based in-game saving did not become commonplace until the 1990s, games for earlier systems emulated by the FunKey S, such as the Nintendo Entertainment System, Master System, TurboGrafx-16, and Sega Genesis, often do not support this type of saving, with many, such as all Atari Lynx games with an in-game save feature, using password-based saves instead. For several dozen NES and Genesis games, however, SRAM ROM hacks can be used to add in-game saving to games that did not originally have it, often replacing more tedious password-based saving systems. Due to an inaccuracy in the Master System emulation of the PicoDrive emulator, however, all in-game, battery-based saves of Master System games are incompatible with the FunKey S.