You can schedule
Disk Defragmenter on
Windows 7 to defragment disks daily. When it is useful?
Windows 7 is set to periodically defrag spinning harddisk out of the box. You do not need to explicitly schedule it.
When is it useful?
I usually leave at the default settings. If you still experience heavy fragmentation (e.g. on a very "busy" disk), consider doing it more often.
The more often you run defrag, the less the files will be fragmented and the quicker the defrag process will finish.
None of this applies to Solid State Disks, or SSDs. Disk seek time on such disks does not suffer from file fragmentation, so defrag will offer no benefit but will accelerate SSD cell wear.
You do not need to defragment every day. About once a month is fine, sometimes not even that is needed. The suggested amount of fragmentation before running the Defrag is 10%. You can analyze each of your disks and only defragment if necessary, or you can just leave it as it is by default and have it run at 1AM every Monday (if you tend to leave your computer on in the night).
If fact, it is believed, that defragmenting your disk too often may have counterproductive results and even damage it in the long run.
Not to mention that in the recent years defrag has been slowly losing the big impact it had on performance. Drives are bigger, more, and it is mostly unnecessary to defrag them unless they are nearly full, which happens less often than it did before. Also, starting Windows 7, Windows has been doing background defrag.
If you'd like some additional information, you can visit the following links:
One thing I heard/read somewhere is that in addition to fragmentation being less of an issue due to increasing disk size, it is also less of an issue because of the insane spin speeds and read speed optimization that has been implemented in HDD's (hard disk drives) manufactured in the past few years. In days gone by, HDD's had relatively low rpm's and little cache on the control board to store 'pre-read' data. This caused the user to experience delays in files and programs loading if they were fragmented and the read/write heads had to run all over the platters to fetch all the little fragments. In those cases de-fragmenting would provide noticeably faster load times for programs and files
Again these days it's mostly a moot point because the disks spin much faster, the drives have the ability to make very good guesses at what bits of data you may want to load next and pre-read that portion of the disk into the cache on the control board, and operating systems have gotten better at doing Defrag operations in the background and keeping relevant files less fragmented in the first place.
All that being said, I still run defrag every two weeks. Mostly because it's a tough habit to break. :)