How much space does a petabyte take up? We know megabyte, gigabyte, terabyte, and now the new word petabyte. A petabyte is just a million CDs. AOL mails out that much every day. No big deal. After petabyte is exabyte, from the Greek prefix exo- meaning excess.
They mail out a million copies of the same information. Now, try putting together a structured database with half a CD's worth of information for every person in the country. Make sure it all matches together, clean up bad data from your input sources, and deliver it in something resembling realtime.