Not 'full' de-fragmentation, Microsoft labs did a study and after 64MB slabs of contiguous files you don't gain much so they don't care about getting gigabytes fully defragmented.
https://web.archive.org/web/20100529025623/http://blogs.tech...
old article on the process
By default, Windows automatically defragments filesystems weekly if necessary. It can be configured in the "defragment and optimize drives" dialog.