Defragmentation: How and Why You Do It
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Defragmentation: How and Why You Do It

A detailed description of what hard drive fragmentation is, why you need to defragment, and how you defragment.


The first thing that the average PC user will do to "speed up" or perform maintenance on their PC is to defragment their hard drive, but very few really know what this means. The first step to understanding to understanding defragmentation is to understand how data is stored on a PC's hard drive. 

Hard drives are split into millions upon millions of spaces known as "sectors." A sector is somewhat like an atom, in the sense that it is the smallest possible space data can be stored in(generally 4KB), and you cannot use half a sector. Induvidual files can use anywhere from one sector, in the case of a short .txt file, or millions of sectors, in the case of a large video game or program.

However, there is no guarantee that all the sectors that are occupied by one file will be right next to each other. For example, let's assume that a 1GB(roughly 250,000 sectors)  file needs to be stored on the hard drive, but there isn't a continuous stretch of 250,00 sectors available because there are thousands of smaller files scattered across the hard drive. In that case chunks of the large file will be stored in different areas of the hard drive, depending on where space is available. This is called fragmentation. 

As you can see, fragmentation affects not only files over 1GB, but any files that occupy multiple sectors. The diagram above shows data on a section of a hard drive, the top one being fragmented, and the bottom being defragmented. Notice the bubble pointing to the SundayParty.JPEG picture file. In the fragmented hard drive, the picture file is split into chunks and stored in two different places, but on the defragmented hard drive, all of the data is stored together.

The computer can open the defragmented file faster because its all in one location. The hard drive uses a rotating needle, similar to an optical drive, to access the data stored on the hard drive, sector by sector. If all the data is stored continuously in one location, the needle can quickly access the data in one sweep. However, if bits of the file are scattered at random across the hard drive, the needle will have to go back and forth between between several sectors in order to read a single file which takes more time. The extra time it takes to read files ultimately causes your computer to lag or exhibit sluggishness.


Defragmenting is done natively in the background if you have Windows Vista, Windows 7, or a Mac. If you have Ubuntu, or any other form of Linux you do not need to defragment at all because Linux uses an efficient file system that does not suffer from fragmentation. If you have an older version of Windows, or want something a little more efficient than the built in defragmentation tool, download Tune Up Utilities. Tune Up Utilities costs money but it defragments and optimizes your PC unlike any other program. 

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