RE: corrupted file
A file corruption in general computing means that a file has not been properly or completely saved, which results often in glitches or complete incapability of use because only a certain percentage of the file actually exists (if you had sufficient knowledge of coding, you could for example selectively corrupt a Word document so that the text doesn't show up when it's loaded). Luckily with a lot of software these days, including Pokémon games, the software always keeps the "recovery" original file that was being overwritten intact as a backup file, so if the new file is being written during a save in a Pokémon game for example, but gets cut off and unfinished for whatever reason, the game will toss the partially complete, corrupted file, and load the safe backup. If that wasn't the case, you'd be seeing things much more strange than Missingno, if the file even worked at all, haha
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