USB memory stick has doubled in size - why?

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http://www.linuxquestions.org РI have an OCZ Mini-Kart USB stick which says 2GB on it, and it has been a 2GB stick for the last 3 years. However, I recently put it into a PC running XP (which had no viruses as far as I am aware) and all of the files in the single subdirectory became corrupted and unreadable. All files at the root of the USB stick were fine, and I could still boot from it (I had Puppy linux installed). I looked to see if the corrupted files in the subdirectory were recoverable, but they were all inaccessible, (with freshly mangled file-names containing multiple copies of the characters '¬' and '=' amongst (HowTos)