do you ever thought that what it means for a disk to fragment, how a disk gets fragmented and how our computers are efficient at locating fragmented files?
for understanding the concept of disk defragmenter, Let's say you're a librarian and you have a room full of encyclopedias. Each has a variety of volumes, each numbered on the end, but each set is colored differently so it's not too hard to tell what book is from what set.
So, a few people come in and take a book from the encyclopedias and take it back to their desk to work on it. Lazy students go, "eh, my set is way over there, but I'll just shove the book here where it fits." Sometimes people are good and put them back; others took both Sa-Sm and Sn-Sz and put them back with the correct set, but in the wrong order. Others stick a blue book with the red ones, a green one with the orange ones, entirely out of order.
Now, you get a shipment of Encyclopedia annuals (remember those?) and you try to add them to the right set, but there's not enough room on that shelf there. And somebody put a thick Volume T where volume Q and R fit, so those two books got shoved someplace else so now there's not any spare room where there used to be some.
Eventually, your encyclopedia room has the books all out of order -- they were arranged for convenience, not for finding, and the longer you go letting things get shoved wherever it's convenient, it becomes harder and harder to find what you're looking for -- more work seeking, less work reading.
Disk Defragmenter/Defragmenting is when you stop and say, "Dammit, I need to put everything back in order, each part in sequential order and only next to directly related volumes, so that I spend less time seeking and more time reading."
Eventually you put it on the calendar, because no matter what you do, eventually people put things wherever it's convenient at the time, new parts come in and get shoved wherever they fit, and thing slowly become out of order over time.
OR
Imagine this. You are an expert valet parking cars. You always group cars by color so you can find them quickly. As the cars come in you put them in the first row one after another and have the first column for blue, second column for red etc. Then the lot starts getting full, but you also have people leaving so you end up with some cars far away at the opposite end and some vacant spaces up near the front. You tell the other valet to start moving the cars to the front where they should be and keep the colors in columns. S/he does this while other cars are still coming and going but it works out. At the end of the day the cars are packed tight and easy to find. That is my analogy for a disk defragmenter.
