Maintaining Your Windows Vista System : Defragmenting Your Hard Disk

File fragmentation is one of those terms that sounds scarier than it actually is. It simply means that a file is stored on your hard disk in scattered, noncontiguous bits. This is a performance drag because it means that when Windows Vista tries to open such a file, it must make several stops to collect the various pieces. If a lot of files are fragmented, it can slow even the fastest hard disk to a crawl.

Why doesn’t Windows Vista just store files contiguously? Recall that Windows Vista stores files on disk in clusters, and that these clusters have a fixed size, depending on the disk’s capacity. Recall too that Windows Vista uses a file directory to keep track of each file’s whereabouts. When you delete a file, Windows Vista doesn’t actually clean out the clusters associated with the file. Instead, it just marks the deleted file’s clusters as unused.

To see how fragmentation occurs, let’s look at an example. Suppose that three files —FIRST.TXT, SECOND.TXT, and THIRD.TXT—are stored on a disk and that they use up four, three, and five clusters, respectively. 

Figure 1. Three files before fragmentation.

If you now delete SECOND.TXT, clusters 5, 6, and 7 become available. But suppose that the next file you save—call it FOURTH.TXT—takes up five clusters. What happens? Well, Windows Vista looks for the first available clusters. It finds that 5, 6, and 7 are free, so it uses them for the first three clusters of FOURTH.TXT. Windows continues and finds that clusters 13 and 14 are free, so it uses them for the final two clusters of FOURTH.TXT. Figure 2 shows how things look now.

Figure 2. A fragmented file.

As you can see, FOURTH.TXT is stored noncontiguously—in other words, it’s fragmented. Although a file fragmented in two pieces isn’t that bad, it’s possible for large files to split into dozens of blocks.

Running the Disk Defragmenter Tool

The good news with Windows Vista is that it configures Disk Defragmenter to run automatically—the default schedule is weekly: every Sunday at 4:00 a.m. This means that you should never need to defragment your system manually. However, you might want to run a defragment before loading a particularly large software program.

Before using Disk Defragmenter, you should perform a couple of housekeeping chores:

• Delete any files from your hard disk that you don’t need, as described in the previous section. Defragmenting junk files only slows down the whole process.

• Check for file system errors by running Check Disk.

Follow these steps to use Disk Defragmenter:

1.	Select Start, All Programs, Accessories, System Tools, Disk Defragmenter. Alternatively, in Windows Explorer, right-click the drive you want to defragment, click Properties, and then display the Tools tab in the dialog box that appears. Click the Defragment Now button. Either way, the Disk Defragmenter window appears, as shown in Figure 3. Figure 3. Use Disk Defragmenter to eliminate file fragmentation and improve hard disk performance.
2.	Click Defragment Now. Windows Vista defragments your hard drives.
3.	When the defragment is complete, click Close.

Changing the Disk Defragmenter Schedule

If you want to run Disk Defragmenter on a different day, at a different time, more often or less often, follow these steps to change the default schedule:

Defragmenting from the Command Line

If you want to schedule a defragment or perform this chore from a batch file, you have to use the DEFRAG command-line utility. (You need an Administrator command line to run DEFRAG. Select Start, All Programs, Accessories, right-click Command Prompt, and then click Run as Administrator.) Here’s the syntax:

DEFRAG 
volume
[-c] [-a] [-f] [-v]