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I asked How to speed up my computer? in another post and one answer was to run disk defrag. I have done this before and in the majority of cases (with multiple computers not just one) it seems to actually slow the computer down vs speeding the computer up. Why is this and what is going on?

Note: I am referring to after the disk defrag is complete. Not while it is running.

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Slower during the defrag, or after it was done? It can take hours to complete on a badly fragmented drive. I also want to take a second and mention that your last couple/few questions have been very general, and not showing signs of much homework being done before asking. You may want to avoid questions that don't involve a problem you're actually encountering, as they may get closed as "Not constructive", or alike. – Ƭᴇcʜιᴇ007 Sep 3 '11 at 0:05
the defrag itself (while running) slows down the disk (and everything that needs it) and gobbles up some ram but afterwards you see some improvements in speed of file accesses – ratchet freak Sep 3 '11 at 0:09
I will be more specific, sometimes when researching there is a lot of info and many times you will read conflicting information. Why I ask here. – L84 Sep 3 '11 at 0:51
The computer is slow AFTER the defrag. I will edit question to reflect that. – L84 Sep 3 '11 at 0:52
Have you benchmarked time and watching disk access metrics to see a) if it's actually slower and b) what is happening when the "slowdown" occurs? – ssube Sep 3 '11 at 1:09
up vote 6 down vote accepted

Every time I hear, "You should defrag your disk!" I roll my eyes and chuckle a bit.

There is absolutely nothing wrong with defragmenting your hard drive. Defragmenting reorders the data on the hard drive so that it is contiguous. "They say" that you will see a noticeable difference in speed, specifically faster. This was more true in the past, than it is now. Modern OSs, drives, and file systems benefit little from defragmentation. Yes, there are some cases where it makes a noticeable difference, but those are rare. Those occur on heavily used file systems where there are lots of writes/deletes going on. However, that is not the typical home or office user. A whole industry has popped up around defragmentation, and I personally feel its mostly snake oil. There are some benefits from advanced defragmenters, like moving data to the innermost track, etc. However, pure defragmention really provides little or no noticeable improvement.

Now as for your computers slowing down after a completed defrag... I honestly believe its not true. I think you are consciously looking for a difference in speed (which probably didnt happen) and therefore, subconsciously you think its slower.

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Thanks, that very well could be true. => – L84 Sep 3 '11 at 1:31

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