Taken from PCWorld Magazine, February 2012 Edition

Back in the bad old days, hard-drive defragmentation was a big deal.  You needed to run a good-quality “defragger” at least once a month to ensure optimal system performance. But times have changed: These days, PCs and drives are so much faster that fragmentation isn’t the problem it once was. What’s more, if you’re a Windows 7 user, you shouldn’t have to worry about fragmentation at all.  Check out these three important facts about hard-drive defragging.

1) Windows 7’s Disk Defragmenter utility runs automatically at scheduled times, usually once per week. This happens by default, so your hard drive is likely already defragged. And by most accounts, the utility’s performance compares favourably with that of third-party alternatives, so don’t buy another defragging tool unless you have specific reasons for doing so.

2) You don’t have to leave your PC on overnight. If Disk Defragmenter isn’t able to run at night, it will kick in the next time your computer is idle.

3) Never defragment a solid-state drive. Doing so can shorten its life span. If your drive is an SSD, be sure to disable scheduled defragmentation in Windows 7.

By the way, if you have an external hard drive that you don’t always keep connected to your PC, it may not get the chance to benefit from Windows’ scheduled defragging.  Run it manually on that drive every month or so.