I have a slow computer, and I can uninstall unused applications, empty the cookies, scrub the registry, do a disk cleanup, and do a defrag, but it is still just kind of slow. If I do a Windows re-install, same OS, and reinstall all of the exact same programs, the computer is pretty fast again.

What exactly is the difference between the fresh and old OS installs?

7 Answers 7


Serverfault question ref: System degredation - does Windows slow down over time?

Mark Russinovich's take on The Case of the Slooooow System
describes how to analyze a slow system.

For personal experience, before a reinstall you could do these things...

Backup all data files (basically leave just the bare windows installation intact)

  1. While I discuss the Windows boot partition; you could clean up the other drives similarly
    • Uninstall all unnecessary applications
    • Cleanup application caches
    • this would be browser caches and such
    • Use autoruns to check what starts with your system
    • take a call on what is required, stop or uninstall as you feel fit
    • Check if you can cleanup the Windows installation a bit more
    • Use RevoUninstaller to cleanup remaining bits
    • Use CCleaner to clean registry
    • Use JkDefrag and move all files to one end of the boot partition (option '-a 6')
    • Disable page file, reboot, re-enable page file to the maximum suggested size
    • use the custom setting to freeze the page file directly to that size
    • You could run JkDefrag once again with defaults ('-a 3'),
      if you feel like it after you restore your backed-up data files

Restore backed up data files.
Check the feel of the system for a couple of days.
You can always go ahead with the re-install/recovery if required after that.
Your data backup would already be in place.

I have used the PageDefrag and Contig tools referred by Molly in the other answer.
These are great tools. But, I have a few opinions,

  1. It is not always useful to run Contig on multiple files of a partition
    • I have found JkDefrag options doing a better job (nothing against Contig here)
    • There are times when removing a Page file and creating a fixed size one in a defraged partition works better than PageDefrag (which cannot do much if your partition is nearly full to start with; again, not a problem of PageDefrag)
    • In the interests of keeping more free-space on the boot partition,
      you might consider moving the pagefile.sys file to another drive (not partition),
      It is suggested by some.

The biggest thing is the file system. Unfortunately, no matter how much you defrag, there are files that will not and can not be organised correctly. As a result, as the computer gets used more and more these files (like the registry, critical system files) grow larger and more fragmented, which leads to reduced performance.

Invalid registry keys are also a big performance problem. Although you've mentioned you cleaned the registry on a regular basis, you have no way to know that what you're doing is actually getting rid of all the invalid keys - unless you want to search through the registry by hand, you're relying on what the author of the tool deems to be invalid.

(That said, registry cleaners like CCleaner are awesome, even if they might miss stuff that I might remove)

Also, the file system can suffer corruption issues over time to - typically people do a format of some description when they reinstall, which replaces the file system, and typically any corruption that goes along with it.

Unfortunately, Windows is like a giant filing cabinet. You can do your best to keep it clean and organized, but eventually you're going to just have to rip your files out and start all over again.

Edit: Molly pointed out some fantastic tools in the comments that may help in defragmenting large system files that aren't normally defraggable (is that even a word) by a normal defrag tool. These tools if used properly, could help in prolonging that reformat.

  • 1
    "no matter how much you defrag, there are files that will not and can not be organised correctly." wrong! the answer to your woes is called Contig. technet.microsoft.com/en-us/sysinternals/bb897428.aspx
    – Molly7244
    Sep 1, 2009 at 16:32
  • How does it work with page files, registry hive files and other large / high traffic system files? Sep 1, 2009 at 16:46
  • 1
    sysinternals have a separate tool for this, called Page Defrag, it will take care of pagefile.sys and registry hives upon reboot.
    – Molly7244
    Sep 1, 2009 at 17:19
  • 1
    you can also manually 'defrag' pagefile.sys. disable VM, boot into safe mode, defragment the drive and re-enable VM. voilá, a contigeous pagefile.sys :)
    – Molly7244
    Sep 1, 2009 at 17:23
  • @Molly: Fair enough. Sep 1, 2009 at 17:39

The disk clean up tools and registry scrubbing tools are conservative, they don't clean as much as they might; they err on the side of leaving items intact in case you need them, because that's better than breaking your machine entirely eg making it unbootable.

If you want to really see the difference, export the registry to a file and use WinMerge or similar to compare the registry from the machine in its two different states.

You can do the same thing with the file system, dir . /s >> textfile.txt to make a file with all the filenames in it.

Also there's the issue of drivers, when you reinstall you will get the default windows drivers, maybe you had a bad driver previously. That can make a big difference, for example, you can get the CD or HDD into PIO mode instead of UDMA mode by mistake or bad drivers, and that would affect it badly.

Don't forget that malware is good at hiding, so you might have had a virus or rootkit that is virtually undetectable, but takes up system resources.

A program that can defrag the pagefile and other files locked by Windows when it is running is PageDfrg.


A complete re-install usually involves reformatting the disk, which means that everything is perfectly clean. The defragmenting of a disk will speed it up only to a point, because some files will not be movable. As well, many programs, when uninstalled, will still leave some of their files behind. Finally, the Registry, although it might have been a good idea at the beginning, is now becoming a mess, and many cleaning programs will be rather careful when cleaning it, leaving still much garbage behind.

Although a re-install involves more time and resources, it will give you a clean setup. If this is something you would plan to redo on a regular basis, I would recommend either running the OS in a VM, which you can install the base once, and replicate, or overwrite. As well, you could do the same thing at the physical level, duplicating a disk partition instead of re-installing.

Also, reformatting the disk to install the OS will remove any spyware/malware that could have been installed in the mean time.


One of the biggest problems with long-lasting installs is basically clutter build-up (of any OS, but Linux/OS X users are generally more tech-savvy, so know how to prevent this) . Windows registry (ok this point isn't every OS, but the rest are), the file system, programs you no longer use, files you don't need, etc.

These take up hard drive space. Over time, that space is not available for:

  • Defragging
  • Swap files (if your HDD is nearly full)
  • Storage

Then there is various bits of crapware that sneak in. Not just spyware, but legitimate programs you might not use, but you have because they're bundled in with other stuff). e.g. If you have Quicktime, iTunes or Safari on Windows, Apple's updater tries to install the other 2 (in fact, AFAIK, it's not possible to get iTunes without Quicktime).

And finally, many uninstallers miss, or deliberately leave files. This is usually helpful (save files for games, config files for software) if you plan on installing it again, but eventually this also builds up.


The short answer is that no matter how much time you spend "cleaning" out Windows, it's still going to be faster to format & reinstall everything. It'll be a huge turning point when this is no longer the case.

On the bright side, I just plan on a reformat every 2-3 years, and use the time I'd otherwise be spending on registry scrubbing, etc. toward automating my reinstall process. (scripting, answer files, etc.)


To answer your question, to make everything perfect again.

To add to the things to do before such drastic measures:

  • Use Revo Uninstaller (when you uninstall something) to minimise registry files left behind.
  • Use Glary Utilities and Eusing registry cleaner.
  • When you do reinstall, get things (programs, settings, ...) as you want them and make a drive image (for example with Drive XML). When your computer is getting slow and glitchy, revert back to this image rather than reinstalling. That'll be a chunk quicker.

You could also remake your registry with a file from Black Viper's site or http://www.speedyvista.com/registry.php Haven't tried this myself but it might help.

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