By default, the disk defrag feature in Windows Vista is set up to defrag your system approximately every four times you restart your computer. It just starts on its own, no matter what you’re working on or what you’re doing on your computer at the time. As you can imagine, that slows your computer down quite a bit. So, if you’d like to speed your system back up by turning the auto-defrag feature off, here’s how you can do it.
First, double click on the Computer icon on your desktop. Once there, right click on your C: drive and choose Properties. Next, hit the Tools tab and then select the option that says “Defragment Now.” (I know that may sound like the opposite of what you should be doing, but stick with me. It will all work out in the end!) Lastly, uncheck the box that says “Run on a schedule.” That will stop all the scheduled defrags from running and from here on out, you can run the defrag whenever it’s convenient for you. Just don’t forget to do it every now and then!
You can also do this in Windows 7 much the same way. Go to Start>Computer then right-click on your C: drive and choose “Properties“. Select the Tools tab and click “Defragment Now…” After that, click “Configure Schedule” and un-check the “Run on a Scedule” box.