It seems to me, with all the gazzilions of bits being read and written, that errors should creep in now and then. So, I was wondering if hard disks (or SSDs' for that matter) use any kind of on-the-fly read/write error checking? You know, a process where the system double checks that each bit written or read is actually who it claims to be. For example, itunes has a "use error correction when importing cds" option in the preferences. I can imagine a computer disk constantly doing this sort of thing. Otherwise, couldn't a single bit flipped the wrong way in, say, a system file cause havoc?