How Did My Hard Disk Become Fragmented and What Can I Do About It?

If you’ve noticed that your computer is slower than it used to be when launching applications or accessing large files, there’s a pretty good chance that what you’re experiencing is data fragmentation on the disk.

Don’t worry.  Even though it sounds really bad (in order to fragment most things you’d have to hit them with a hammer) file fragmentation is both common and easy to fix.

What Happened

Early computer storage media, usually huge reels of magnetic tape, were sequential access storage devices. Like listening to music on a cassette tape, in order to listen to the third song you’ve recorded, you have to listen, or at least fast forward though, the first two.

Your hard disk is a random access storage device.  It has a read/write head that can jump back and forth across the magnetic platter inside and touch any part of the disk it needs – it’s quite like using a CD player in that you can access track 3 simply by pressing a button.

When you first got your computer, it likely had an operating system like Microsoft Windows installed on it, and you loaded your own application programs and files on it all at once.  Hard disk performance was optimal, because there hadn’t yet been an opportunity for fragmentation to occur.

Fragmentation occurs when files are deleted from their nice, orderly position on the hard disk, leaving “holes” of empty space in the file system.  These holes don’t tend to become a problem until the “clean” empty space on the disk gets filled up, and then the computer starts looking for spaces in the “holes” to put data in them.

If the computer can’t find a space big enough for a file, it will have to split the file up into two or more segments, and put the pieces into separate locations on the drive.  A split, or “fragmented” file while have a small impact on drive performance.  Many fragmented files will slow your hard disk noticeably, impacting negatively on your computer’s performance, especially when loading programs or accessing files.

The Disk Defragmenter

Windows comes with a disk defragmentation tool that works quite well. In Windows Vista/7, access from the Start Menu, through All Programs>Accessories>System Tools.  In Windows XP, simply type “defrag” from the Run dialog on the Start menu.

When the Disk Defragmenter opens, it will give you a quick summary of the number of hard disks on your computer (not that logical disks are treated separately, so if you have your drive partitions, the Defragmenter will see each partition as its own drive), and their state of fragmentation.

If this quick status shows any fragmentation at all, choose the “Analyze” button for that drive, and allow the software to further analyze your hard disk contents.  It will take a few moments to finish, and in the end will report on the state of your drive, and it will recommend a defragmentation if needed.  Note that you can choose to defragment even if Windows doesn’t recommend it, but as the process takes a long time, it might not be worth it.


Defragmenting the drive is a very complex process, and it takes quite a while.  Windows moves files around on the hard disk, trying to achieve a state as close as possible to a fresh installation of all the programs and files on your computer.

In order for the defragmenter to do its work, it will require that your disk drive have a minimum of 15% of free space.  If the disk is too full, you will have to delete some files before you can use the program.

Automating the Defragmenter

Fortunately, the Disk Defragmenter has a scheduling tool built in.  It’s recommended that you defrag your disks on a regular basis, especially if you add and delete files on a regular basis.

Click on “Schedule” and choose a frequency and a start time, preferably when you know the computer will be on, but aren’t likely to be using it.

Disk defragmentation should be done on a monthly basis at minimum.  If the drive is always in need of a defrag, do it more frequently.

Leave a Reply

© 2012 why is my computer so slow. All rights reserved.