[CentOS] differnt results between df and ls

Thu Mar 29 10:48:07 UTC 2007
Tom Brown <tom at ng23.net>

Hi

this is more than likely a general linux question but on a CentOS4 box 
whats going on here?

# ls -al foo.txt
-r--r--r--  1 xxx xxx 1373149856 Mar 28 04:34 foo.txt

# du -sh foo.txt
808M    foo.txt

any ideas ?