I'm going to assume that you're a Windows user, and if not, then a Mac user. In brief, unless you know Linux or at least get into the hang of individual things you can learn in these forums, they're stored somewhere you can't get to. If you google this forum for mmc install os (or something like that), you'll find how to install them onto a SD card. But if you don't fiddle a lot, they're stored in the N800's internal flash memory (i.e., not on a card). It turns out, though, that the apps are so efficient in byte-usage that there is plenty of room there unless you go wild.