Disk Defragment instant?

I have Windows 7 64-bit OS. i havnt defragged in a while so i know i need it but when i go to Disk Defrag it shows 0% fragmented and it analyzes and defrags in literally 1 second. i asked a friend and he mentioned something about windows 7 having some sort of automatic filing system to reduce fragmentation but i still feel like something isnt right what could be the problem?