To the average computer user, the file on their disc is a single entity. Its just a.. thing.. you open it, you close it, you work on it and you save it and thats it. its very much like a paperback book. No frills and nothing to worry about. Whoops.. guess what..
That file is rather like a paperback book, but not for the reasons that you think.

It has individual pages and the computer has to keep them all tied together to make it stay a book, rather than separate pages that are scattered around the hard drive.

A windows hard drive is just a big collection of drawers built expressly for holding information. All of that information is stuck in a different..  drawer.. for lack of a better term. Every drawer is about the same size, each about 500 bytes, so that when you put a file on your hard drive, windows sticks it enough drawers to hold it. So that, if it is only 5 bytes in size, it still will use up one of those 500 byte( the actual number, if you care is 512) “drawers”, using up one byte of space and leaving 499 unused. If it is 520 bytes, it is assigned two drawers, filling up one and part of another one. Leaving in the second one, about 480 spare bytes, give or take.


It isn’t really ncessary for the drawers to be next to each other. In reality thats what the Random, in RAS, or Random Acess Storage is for. The data can be stacked in drawers that are not next to each other.
But Windows, when it makes the file, keeps track of which drawer they are in, so that whereever they are on your disk, Windows can open the right drawer, very much like the page number.

Envision this. If you have a drawer in your home with pages of a report thats due, and each page is in a different drawer, and you know where they are  but you have to go and retrieve each one before you can turn in the report, its going to take some time right? Likewise with windows trying to recover  a fragmented file so you can use it. Its going to take a lot longer.
If, your pages are stacked neatly in those drawers, getting them out takes a lot less time, because all you need to do is open the drawer. Thats all windows has to do to retrieve the clusters .. or pages of information in a file thats on a hard drive that is not fragmented, which is why we defragment our files.

It’s easy to do, doesn’t take  all that long and should be done about weekly. You can set it up to happen while you’re sleeping so that the computer never gets fragmented at all.
Go to Start, then  Accessories-> System Tools-> then Scheduled Tasks and set it up at a time thats convenient to you