Getting Technical:  Drive defragging

April 2 2008

If the slowly lengthening days have you thinking about spring cleaning, don’t forget your hard drive! “Defragging” your disk is as good as reorganizing the garage when it comes to making things easier to find.

Modern hard drives have multiple disks (“platters”), each with thousands of “tracks” (concentric rings) accessed by a drive head that moves back and forth across the platter (see illustration). image

As you store files on your hard drive, your operating system slots them into open sections (“sectors) of track. Some files are small enough to fit all in one sector. Others, however, are like multi-volume book sets — they require multiple slots, or “clusters” of sectors.

Naturally, your system prefers to store parts of a file together on the disk. It’s easier to keep them associated that way. But if the system can’t find enough adjacent clusters open, it will “fragment” the data into pieces and put them wherever it can find room.

As you can imagine, this makes the file harder both to put away and to retrieve. A central file-storage system keeps tabs on where (on the drive) each fragment is stored, but the drive heads have to run around the whole drive looking for the scattered pieces. Performance and reliability suffer.

What increases fragmentation? The more you add, delete, and edit files, the more fragmented your disk storage gets. Having your hard drive close to capacity also forces the file-management system to spread things out more as it fits new items in.

Defragging is like taking all the books off the bookshelf and putting them back with the related ones grouped together again. In the hard drive’s memory structure, defragging improves the speed and reliability of your system. The process (using the defragging utility in your system) can take up to several hours, depending on degree of fragmentation. It’s a good process to start before you head home for the day.

A successful defrag will improve your hard drive’s performance. It might even embolden you to tackle that hallway closet next!