General Question

Rickover's avatar

What is disk defragmentation?

Asked by Rickover (110points) October 2nd, 2010

What is disk defragmentation?I do not know much about computers.My friend told me that if my computer becomes slow i should defragment my disk.Is it true?

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10 Answers

Ame_Evil's avatar

Disc fragmentation happens when you constantly delete files and make new ones. Defragmentation is a way to bring files back together and make things load faster.

Say for example you have the following files:


You delete files D in the middle which leaves you with a gap:


Then you want to add news file H. H is too large to fit in the gap, so part of the files have to be added to the end as well as filling in the gap:


What disc defragmentation does is move the files around so that common files are together. So in our case it may do this:


A good tool I would recommend to do this is: rather than the standard Microsoft tool. It’s free and easy to use :).

Source: and others

RareDenver's avatar

I was about to explain it but @Ame_Evil has just done a wonderful job

Ame_Evil's avatar

@RareDenver ^_^.

Another point I would like to make: partitioning drives helps reduce some problems of fragmenting and the defragmentation process. For example if you have a 1TB hard drive you may want to partition it as 200GB and 800GB, using the 200GB for files which are constantly deleted and rewritten, and using the rest for files that are more stable (like movies, music, games). This allows for defragging to be much faster as there is less files to be moved around.

Most sources recommend to split into further partitions, but its mostly a personal preference and mostly depends what you use your computer for.

And another thing… use before defragmenting to free up some hard drive space. Don’t fiddle with the registry stuff as you said that you don’t know anything about computers.

Thammuz's avatar

As a side note, since everything to be said about defragmentation has already been said, if you’re using windows then defragmenting the disk is probably not going to give you such a big speed boost, your problems are more likely of a different nature, expecially if you have installed windows more than one or two years back.

mrentropy's avatar

Defragging a hard drive was more useful back in the day when hard drives had little or no cache, were slower, and the brontosaurus roamed the Earth. If you see much of a speed difference with a modern drive I’d be surprised.

Also, as far as I know, the Windows tool won’t defrag the page file (your virtual memory) and if you don’t have a lot of physical memory that’s where a lot of slow down will come from, reading and writing to that file. Not so bad if it’s a fixed sized, but a pain if it’s set to grow and shrink as needed.

john65pennington's avatar

Ame Evil great and correct answer. great explanation. plus one for you.

jrpowell's avatar

Just a note. If you use OS X 10.3 or above you don’t need to defrag. It is built into the OS and it just does it when a file won’t fit. *Files need to be over 20Megs to be auto defraged.

jerv's avatar

I have generally found the speed gains from defragging to be pretty meager with a modern computer. It used to mean a lot more back in the days of 50MHz CPUs and hard drives measured in megabytes, but I haven’t had nearly as much benefit from defragging since getting a computer built in this century.
Still, it does help a bit so I still do it, but fragmentation won’t slow your computer down nearly as much as malware, having too little RAM, or running Vista will.

@Ame_Evil Great job!

@johnpowell Or you could just run Linux :P

@mrentropy I actually had a defrag tool that would defrag the VM file, though it required a restart and did it on the next boot. Still, it is best to set the swap file size yourself.

rimm's avatar

Disk defragmentation is a way of speeding up the data access by reorganizing the files that get fragmented and placing them in an orderly way in which the HDD can read them faster. But dont wait till your PC gets slow to defragment. Considering the fact that the Windows dferagger is slow and is not efficient in defragging severely fragmented disks (especially in low free space), you are better off keeping fragmentation at the lowest possible levels proactively.

mr_universe's avatar

I would think from experience, organizes fragmented files that which are from files from daily use are brought up into memory and then stored on the surface which over time slows down the process of the virtual machine if not defragmented

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