You have 2 options for the funtion you are looking for in PD.
1) Check the Boot Time Box, and reboot.
2) Right Click the Drive you wish to Defragment system Files on, and youll get a menu.
As mentioned, most system files it can Defragment without rebooting. But the PF will need a reboot.
As far as Im aware, Win7s does the system Files only.