Understanding Disk Fragmentation

Let's talk about laundry. When you have a pile of shirts, a pile of shorts, a neat pile of sheets and one of pillowcases it is easy to get dressed in the morning. You get a shirt from the shirt shelf. You know to look in your underwear drawer for the shorts. It takes a minute to get dressed.

On another day all your clothes are together in a big hamper. You find a shirt, search for a pair of pants you can't find a matching pair of socks!!! It takes an hour before you are finished.

That laundry is a lot like your hard disk. Files are stores in smaller pieces, clusters of data. When all the parts of each file are next to each other the disk runs at optimum speed. When the pieces of a file are strewn all over the disk it runs slower, because the drive has to find all the different parts and put them on a shelf whenever you load that file.

How does a disk become fragmented? When you delete a file it leaves a space on the disk that can now be used to store a new file. That space might be between two other files. If the next file you save is bigger than the one you deleted, parts of it will take the old file's place, but the rest has to go somewhere else because the next file is already in the next slot.

You know those playground whirl-a-gigs that go around and around and around and you have to hold on for dear life to stay on? When you are on the outside where you can run around and jump on, you travel farther than if you were riding in the middle. This means that if you want to tag a lot of people it is faster to tag them near the center. Your hard drive can find data faster near the center of its disk, too, for the same reason that data is closer together. There is a mechanical arm that searches the disk for files and their parts. The less it has to move, the faster your files are accessed.

So we have two conditions that can make your hard drive work faster or slower:

1. Whether or not all the pieces of a file are near each other
2. The physical location of files on the actual disk

Since we tend to run programs more often than we access data, it is best to store program files closer to the center, then work your way outward on the disk with data. If you are afraid this is getting too technical or that I am going to tell you that you have to do this yourself, take heart. Windows comes with a disk defragmentation program. In XP click Start > All Programs > Accessories > System Tools > Disk Defragmenter.

When the program starts you see representations of the disks and/or partitions (a partition is a portion of a disk that Windows has been fooled into thinking is a separate drive) along with some information about the disks. You will also see a series of buttons. Two of these are important: Analyze and Defragment. Click on a drive to highlight it in the list and then click one of these two buttons.You don't have to analyze a drive before defragmenting, but it is worth it because you may find that you don't have to defragment the drive after all. If, after analyzing, the program suggests you defragment that drive, click the Defragment button.

Do this when you don't have a lot of work to do, because it will work better if other programs aren't accessing data at the same time. It is also likely to take some time. Here's why: the program starts at the beginning and finds all the parts of the first file. It temporarily stores the parts it finds as it clears space at the beginning of the disk (near the center). The program will tell you what percent of the job is done as it goes along. Once it has cleared the space, it rewrites the files with all their pieces together. Defragmenters typically put programs first, then data. When it is done, it is as if someone had shelved all your laundry exactly where it is supposed to go. Next time you need a shirt, you can get it quickly because you will know exactly where to find it, and you won't find the sleeves on a different shelf from the rest of the shirt! As for your computer, you will notice that there is less lag time between clicking a shortcut and loading the program.