Why do we Defrag the Hard disk?

What is Defragging?

Defragging is process done to a hard disk in order to improve performance and recover some lost disk space. Defragging is an essential part of a PC's upkeep as it keeps all the data on your hard disk in an easily readable order. If a hard disk is left without defragging, then over time the disk will begin to lose performance and also slowly reduce the available capacity to data. As you will be aware if your hard disk is running slowly then this will affect the rest of the system performance, in all applications and especially in games, where frame rate is important.

How does Defragging improve performance?

When you defrag your hard disk you re-arrange the order in which the data is stored on the drive. The PC will arrange the data so that data that belongs together and needs to be read together is actually put in the same place on the drive. The obvious question here is why doesn't the PC store the data in the correct way in the first place? In an ideal situation (such as a blank disk) the PC would do these as a first option. However with the amount of data being deleted and wrote to the disk every second the PC is on it is no wonder that the data cannot be stored together.

Lets have a look at an example. Say you write 3 files to a disk all 10Mb in size the data would look like this when written to a blank disk.

This is how your PC would prefer to store the data for maximum performance. It stands to reason that this is how you would like it to be stored as well if you needed to search for the data. But now lets say that you decide to delete file 2 as its no longer any use to you. The disk would look like this.

You now have a file 4 that is being written to the disk, but this time the file 15Mb in size. When the PC stores the data on the hard disk this time, its not as easy.

<> This time the PC was unable to keep the 4th file intact as the space left by file 2 was only 10Mb in size and file 4 was 15Mb in size. Now the PC has had to attach the final 5mb of file to the end of file 3 where the rest of the free space is. As you can imagine with the millions of files being written to and deleted from the disk each day, not to mention the temporary files that windows uses on a frequent basis its not hard to imagine the state in which your hard disk can be in after months of use. After a defrag in this simple example your PC would re-arrange the disk to look as follows.

When files or indeed groups of files that belong together are stores next to each other the PC has a much easier time locating the data plus the disk heads don't have to travel to different parts of the disk to retrieve the data required. This of course speeds up the disks performance and so in turn increases overall system performance. There are of course levels of performance gains. It becomes more negligible as you move to faster hard disks with large memory buffers to compensate for file fragmentation however I would not ignore the problem of fragmentation, it doesn't take much effort to defrag your disk now and then

How does defragging increase disk space?

Simply put defragging doesn't really create any free space on your hard disk. It may appear when you look at the graphics that defrag programs show you, that the disk looks like it has more space, but all you are doing is moving data about not removing any. Any disk space gain is negligible and is caused when the defrag program puts together half clusters of data. Clusters can hold a number of files, but if not filled the next file is started at the next cluster. If a file is broken into pieces around the disk and defrag can put the file back into a single cluster, or just save a cluster somewhere a small amount of space will be released.

Advanced Defragging

Some defragging software can go a little beyond just sorting your files so they are all together. Programs such as Norton Speed Disk can also sort your entire sets of files and programs into the order that they are used. For example it can be set so that your windows swap file is at the fastest part of the disk, followed by games and most used applications which also need the fastest part of the hard disk., Then documents etc and rarely used application can be put to the back of the disk., This gives the priority speed access to the applications that need it most. Again this may only be a small increase in performance but every little helps.

Software to use for Defragging

You will be pleased to know that Windows comes with an adequate defrag program which everyone can use. There are also some other pieces of software out there for a more specific use. Norton Speed disk is one option on the market which comes as part of Norton Utilities and Norton Systemworks. Doing a search on Defrag software on your favourite search engine will give you some options of free to use and pay for software.