You... kinda deleted the OS.
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The TI-Nspire OS is around 9 MBs (see
here), and deleting something arbitrary like "os.img"... well, I don't know what you were expecting.
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What's interesting though is that you got to see this "os.img". Could you tell us
exactly how you did all of this, what you saw, etc.? Be VERY descriptive - you might have found an interesting bug for us to play with.
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Anyway, just reinstall, and don't delete os.img
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For TI-8x games, no, we don't have a working emulator yet. calc84maniac had a project like that, but he lost all the source code.
I might port SDLWabbitemu to the Nspire, but it would be kinda slow... only time will tell.