The short answer: Defragging isn’t vital anymore, but it’s still a good idea–unless you have a solid state drive. And Windows’ own defragger is fine.
As you use a computer, files get split up into fragments. Windows may show you that a file is in My Documents, but physically, bits and pieces of it may be scattered across the surface of the hard drive’s multiple platters. All this fragmentation theoretically slows down the PC. When you defrag your hard drive, the files are physically moved so that as many of them as possible are contiguous.
I reviewed defraggers for a big utilities roundup about nine years ago (you’ll find the defragger section here). The PC World Test Center ran a test for that article to discover which defragger best improved system performance. All of the defraggers came in at a statistical dead heat. Even weirder, the still-fragmented disk tied with the defragged ones.
In other words, defragging didn’t improved the PC’s speed at all. I was so skeptical of those results that I designed and ran my own test, concentrating on tasks that fragmentation would likely slow down. I got the same results.
So I asked Steve Gibson of Gibson Research, a major authority on hard drives, about these results. He told me that modern hard drives were not noticeably slowed by fragmentation (and remember, this is modern as of 2001). He added that defragging is still a good idea, because, should a disaster strike, it makes successful data recovery more likely.
I checked with Gibson again while researching this post. As far as defragging hard drives is concerned, the situation hasn’t changed. But he warned me about defragging solid state drives (SSDs). Since SSDs wear out from too much writing, but not from too much reading, defragging (which does a lot of writing) will shorten their lifespan. “I would definitely defragment once after getting the entire system setup,” Gibson told me, speaking specifically about SSDs. “And then perhaps annually after performing major updates and housekeeping.”
For a hard drive, I generally recommend defragging about once a month–with Windows’ own defragger.