Windows Pane Relief: Picking Up The Pieces with Disk Defragmenters
Disk defragmenters are little understood, much misunderstood and about as glamorous as taking out the trash. However like taking out the trash, disk defragmentation is something you've got to do if you don't want to drown in your own waste.
What's a Disk Defragmenter?
To store information efficiently on a hard disk, Windows deals with files in chunks called clusters. The default cluster size is 4K, and anything written to the disk occupies at least one cluster (4K) of space. As much as possible, Windows tries to lay down the clusters contiguously (i.e., one after the other) on the logical disk. The operating system maintains a table for itself, showing where everything is on the logical disk and recording what space is available for new files. If there aren't enough contiguous clusters available on the disk, Windows splits the files among the available chunks of space.
However, files aren't static. We constantly add information to files and delete them. Adding information to a file requires additional clusters, and those clusters probably won't be contiguous with the original group of clusters. Deleting files or parts of files frees clusters (or groups of clusters) which may be in the middle of clusters in use. This process of chopping up the available disk space is what we mean by fragmentation of the logical disk.
Disk defragmenters keep your drive operating efficiently by searching out the bits and pieces of files scattered over your disk partitions and moving them around so they are next to each other on the logical drive. Disk defragmentation is a vital part of maintaining a healthy Windows system. Since a badly fragmented disk can increase input-output (I/O) times by 60 to 100 percent or more, Windows disks need to be defragmented regularly to maintain system performance. If you're administering a Windows system, that means you need a third-party disk defragmentation program.
You may have noticed that I emphasize the term logical disk. One of the most potent points of confusion about disk defragmenters is the idea that they deal directly with what is actually written on the platters of the hard disk. They don't, at least not any more.
The truth is that Windows, or any other major modern operating system, doesn't have the faintest idea where anything is physically stored on the disk. The operating system deals with an abstraction called a logical disk; it is the job of the disk controller to take that logical disk and decide where to actually write the information on the disk.
Modern hard disk controllers are pretty remarkable gadgets, and you could easily write a book about how they work. For our purposes, it's enough to know that they take that logical disk map from the operating system and write the information onto the physical disk where it seems best to them.