How Defragmentation Speeds Up the PC - dummies

By Dan Gookin

To understand defragmentation — or defragging as it is commonly known — you must first understand fragmentation. All storage media has some level of fragmentation and, honestly, it’s beneficial. It’s too much fragmentation that slows down your computer. The short answer: Defragging is a way to speed up your PC.

Fragmentation occurs when a computer file isn’t stored as a single chunk of information. Instead, the file is split — stored in two different spots on the drive. The file is fragmented.

To help you form a picture of how file fragmentation works, think of your PC’s hard drive as a parking lot surrounding a large municipal stadium.


A parking lot is basically asphalt. For the parking lot to function, it must be painted with spaces. A similar thing happens to the hard disk surface. The painting of “parking spaces” on a disk is called formatting. Without parking spaces or formatting, cars and files wouldn’t know where to go. Chaos would ensue.

Now pretend it’s an hour before game time. The parking lot is beginning to fill. Cars come in one side of the parking lot and are directed by cheerful parking lot attendants to fill the empty spaces in an orderly manner. Each car is parked next to another car.


Your PC’s hard drive fills with files in a similar manner: Files are placed on the media one after the other, just like the cars.

On your computer, you probably delete a file now and then, or you uninstall a program. Windows itself creates and deletes temporary files all the time. If this situation were duplicated in the stadium parking lot, you would see empty parking spaces where cars have left.


In order to make use of available space, the operating system begins to split up, or fragment, new files stored on the hard drive. So, when a new file is added to the hard drive, the operating system fits it into the available empty space. If the file fits, great. If the file doesn’t fit, the operating system splits the file into smaller chunks that do fit. That’s fragmentation.

The operating system reassembles the file’s pieces into a single whole when the file is accessed. A tad more overhead is involved, however, in reassembling a file’s fragments.

As you continue to use the hard drive, more and more files are split up to take advantage of the available space. More fragments equals more overhead to reassemble the files when they’re loaded or saved. The result of that overhead is sluggish disk performance.

The solution to the fragmentation problem is to use a defragmentation, or defrag, utility to put all files stored on disk into non-fragmented chunks and remove the empty spaces between the files.

Some defragmentation utilities may even do a third task: Relocate important and frequently accessed files to the start of the disk. Such a feature greatly improves disk performance.

The moral of this story is that fragmentation is a good and necessary thing. To keep your PC’s hard drive working at maximum efficiency, it should be regularly defragmented.

  • Do not defragment SSDs, media cards, or thumb drives! Sure, they get fragmented, but their speed is fast enough that the fragmentation doesn’t diminish performance.

  • The PC’s storage media always contains some fragmentation. That’s just the nature of the business of storing files on a computer. Too much fragmentation, however, leads to sluggish performance. Regular hard drive maintenance must include some type of disk defragmentation.