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I have heard that you should keep the registry clean on Windows. Is this actually important or is it just myth?

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Is there a way to "defragment" the registry? Rewrite to remove unused space? –  Agnel Kurian Jun 17 '10 at 9:40
    
Well, it's obviously worth it to the companies that sell such cleaning tools for money. –  Michael Kjörling Sep 26 '13 at 14:05
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11 Answers 11

I've used PC HealthBoost with success on a few slow PCs. I chose it because it does work as advertised and is in good standing with Microsoft. Microsoft, itself, also used to make a registry cleaner called regclean.exe.

Basically, uninstallers sometimes are poorly written, and that sometimes creates errors in your operating system that show popup errors or blue screens. Also, have you ever right-clicked the desktop and found it takes a long time because the context menu has extra menu options from a product (like Norton Antivirus) and one of those menu items is still there but the product has since been uninstalled? That delay is aggravating, and contributes to the slowness of the PC. Also, when a PC boots, it is looking for file paths mapped to keys where those files were deleted by an uninstaller but not the key.

Some may say it's only a marginal slowness, but I've seen it be a significant factor with nothing more than 4 poorly written uninstallers, where some of these programs may have created dozens of registry keys.

A word of caution, however -- not all registry cleaners are alike. You want one that can backup your registry first before making changes, and one that doesn't delete legitimate keys. Some of these companies are cagey, but I've been very pleased with PC HealthBoost.

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I checked the Wikipedia page on registry cleaners.
Looking at Jeff's answer, maybe someone needs to update that with criticisms.

I have used CCleaner often, and in fact, also been suggested registry defragmentation tools.
Mark Russinovich, who I trust a lot with my Windows machines, also has a PageDefrag tool that works on registry hive defragmentation.

A reference to another tool by Mark called RegDelNull that helps to cleanup registry keys with embedded NULL characters.

I also often use **RevoUninstaer to cleanup after some uninstalls.
The warning from Mark and others on the risk involved with cleanup is taken seriously.

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+1 for PageDefrag, although it gets a much bigger bang from defragging the page file than defragging the registry. –  Jeff Leonard Jul 15 '09 at 18:04
    
@Jeff, Very much so!! Page Files are easier fruit when allowed to grow (vary in size). Its always better to fix them at a suitable size once and for all. –  nik Jul 15 '09 at 18:11
    
Also, I would guess that the bang from defragging the hives is much bigger than from cleaning out dead entries. I don't have evidence to cite, though. –  RBerteig Jul 28 '09 at 22:56
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I believe it's better (effort and time wise) to just reinstall the whole system every 6 months or so, than spend every once in a while cleaning registry, "keeping the system clear" with anti virus, anti trojan, anti spyware, anti ... whatever you have left.

And the whole reinstall doesn't take more than 4-5 hours, including installing all software and customizing preferences in it.

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I don't agree with this....I have a serious number of applications and programs and 4-5 hours would not cut it. Try something on the order of 1-2 months to get my system back to what I wanted after the last Windows 7 wipeout. –  mdpc Feb 11 '13 at 18:27
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Well, cleaning the registry from entries virii, trojans and spyware leave there is certainly not a bad thing to do, even if regular cleaning from stale entries doesn't give much benefit.

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I agree, cleaning the registry risk vs reward is low, however tools to Registry defrag / compact the registry will increase performance. I use Registry Mechanic to just defrag and compact the Registry, not the registry cleaner options.

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The registry is a huge database optimized for speed. It doesn't matter if some game left its config options in there. Other programs aren't going to care and Windows can handle the memory usage just fine by paging (i.e. only loading what's needed) and other techniques.

The only time a registry cleaner could be useful is if a program was not uninstalled properly; in this case you might have some specific problem such as a broken file association. But if you are not seeing problems and are just looking for speed you are probably wasting your time. Not only that, but deleting stuff from the registry can break things in subtle or hard-to-fix ways. Hopefully a good registry cleaner backs up all its changes so that you can easily restore your old registry... assuming your computer boots properly after the cleaning.

If your windows system has lots of strange bugs that are due to registry problems you might be better served by re-installing. Before XP I used to re-install Windows every 6 months. Now I almost never have to do it. I would avoid registry cleaners.

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+1 for the failed installation point. That seems a valid reason to use some kind of tool to clean up. –  Jeff Yates Jul 15 '09 at 14:22
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+1 for "Before XP..." The only XP crashes I've seen have been my own fault caused by foolishly testing a buggy driver I was writing on my development machine instead of insisting on having a second disposable machine for the purpose. –  RBerteig Jul 28 '09 at 22:55
    
Do you have a citation that the registry is optimized for speed? This certainly does not appear to be the case. The registry files can become fragmented and in any case, it seems to be a fairly simple format, not optimised at all for fast lookups. I have no idea about how the data is stored in memory, however. Perhaps registry retrievals are O(1) rather than O(log n) or O(n), I just can't find any reference to support this. –  ChrisInEdmonton Jul 30 '09 at 17:07
    
I'd argue that a better way to deal with a failed installation is to re-install it correctly and then uninstall it. That way you won't be deleting random keys which end up breaking your computer. –  Richard Sep 14 '12 at 18:07
    
@Richard: I was referring to a failed uninstallation, where there is left-over stuff in the registry in places where it affects other programs. Such as file associations, COM object registries, etc. A registry cleaner can find such orphan links and delete them. It's probably the only valid use-case for registry cleaners I can think of. And in the last 10 years I'm not sure I can recall ever needing to fix such a failed uninstall. –  Mr. Shiny and New 安宇 Sep 15 '12 at 21:12
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there are few good things that a registry cleaner can do. One is removing file association to uninstalled programs for example.

But I haven't heard of any benchmark that demonstrates that cleaning your registry will increase the overall performance of your system.

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Not only is cleaning up the registry of minimal impact to your computer's performance, there is also a high chance of doing serious damage when attempting to do so!

I recommend NOT doing this unless you have a valid reason to do so.

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CCleaner can find and remove hundred of invalid registry keys. If anything, I think cleaning the registry of invalid references can be good if you want to avoid having conflicts between software that is installed on the machine.

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I'm probably not a typical user, but I've never done so and never seen a need to do so. However, I do know that pretty much every program you've ever installed leaves some kind of junk lying around in your registry and/or hard drive, so it's still possible that such utilities might have a purpose.

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up vote 50 down vote accepted

As I understand it, cleaning the registry is not going to really do much for your computer performance if anything. The registry contains thousands of keys and cleaning out a few dead ones won't really make much difference.

This forum post contains some sources that seem to confirm registry cleaning as a mythical performance enhancer.

It will have no effect on system speed. There is an excellent chance it will make your system less reliable.

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+1 for the link to Mark's quote I regularly use cleaning tools, but I am more oriented to clean temporary files and program caches –  Drake Jul 15 '09 at 14:17
    
I'd upvote this answer if I had any more votes left today. :) –  Marc Reside Jul 15 '09 at 14:19
    
I agree for the most part, but the real answer is "it depends" I haven't needed to clean my registry for several years now –  David Hayes Jul 15 '09 at 14:58
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@Agnel: With Mark Russinovich's PageDefrag. –  Joey Nov 26 '10 at 11:26
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Microsoft has even stated the registry cleaning tools are not useful. I believe them, because if it was useful, they would have made their own tool. –  Keltari Sep 14 '12 at 17:42
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