What is 'defragging', and why should I do it?

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Couple of points of clarification.
Defrag CAN free up some space in 2 ways. But you shouldn't count it happening, or expect much space to be freed up.
First, depending on how the fragmentation happened, each fragment could have "freespace" intended by the file system for growth. So when the file is defragged the only freespace left is at the end of the file.

The other way defrag can free up space is if there are many small unsed spots on the drive, the file system may not use them until they are "joined" together into a larger block of freespace.

On the question of locked files, the more "advanced" (than the stripped down defrag tool bundled with Win) defrag tools that can handle locked files. They perform defrag in several discrete steps. One of the later steps is to do a reboot and run a defrag BEFORE the OS and/or "startup" apps are loaded.

As well, when HD free space is less than 20% Windows can get twitchy. Strange, unexpected, things can happen such as defrag programs abending unexpectedly. It's not as common a problem these days as it was when HD size was measured in MB not GB.

I defragmented my drive and it improved the speed a lot. I used the trial version of Diskeeper09 which a friend suggested. Its really easy to use as its automatic.

I have Vista and the when attempting to save as c:\defragit.cmd, a box pops up stating "you do not have permission to save in this location. Contact the administrator to obtain permission."
What does this mean and how do i obtain permission?

\\john system is not accessible you might not have permission to use this
network resourece.contact the administrator of this server to find out if
you have access permissions.the server service is not started..

this errore coming my network pc... what solution
..reply me...

defragment works but sometimes, it also creates problem especially with videos. wats the problem

I would seriously recommend the "Piriform Defraggler" for this, free to download and a really good programme, they also have a Ccleaner which cleans out spyware and generally makes your computer run faster, just google piriform if your interested, really good stuff!

Hi Leo, you're so wonderful. Thank you. After I defrag and when I view the undefragged files, it just says they're in my documents but doesn't tell me which ones. How do I find them?

Also, maybe you can answer both of these at the same time. I have another computer that will defrag, but there's a great deal of free space in between the compressed files. Why?

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