Are Registry Cleaners Worth Running?

Over the last couple of days, a minor debate has raged over whether Windows registry cleaning software is useful or whether it's garbage. This Digg discussion says it's junk, while this one has posts from those who say otherwise. Based on the number of diggs, the yeas have a considerable lead. But I thought I'd see for myself if I could find out if registry cleaners have a genuine positive effect.

I'll admit upfront that this test was only quasi-scientific. The problem with measuring what a registry cleaner does is that the results are not easily repeatable. Every machine is going to have a different set of junk in its registry, so comparing results from one system to another will not always make sense. Nonetheless, I wanted to at least provide a data point for the argument based on one system's experience with cleaning the registry.

Registry cleaners work by removing outdated and incorrect entries from the Windows registry, the OS's repository for all system settings. It dates back to Windows 3.11, and with each new version of Windows, it has grown in complexity. Installing, re-installing, and un-installing a lot of software, plus the toll taken by simple daily use of Windows, leads to the registry growing in size thanks to entries that don't get properly deleted or updated. Over time, the registry gets bloated, and some people say that this registry bloat leads to poor performance and general system instability. Thus, the registry cleaner was invented.

So on to my test. Two of my PCs have had XP reinstalled from scratch in the last couple of months, so their registries should not be bloated. Instead, I used as my test system an old Windows 2000 box which hasn't been reformatted for years and which I use to install all kinds of test software, including spyware and viruses (for testing security software). If any machine has a messed-up registry, it's this one.

I measured boot time (during which the registry is accessed the most) to see whether registry cleaners would have any positive effect.

Sure enough, this machine was dog slow. From a standard cold boot, the OS wasn't usable until 2 minutes, 30 seconds, and constant hard drive activity didn't stop until a whopping 5 minutes, 19 seconds. That's insane!

For test #1 I installed the popular CCleaner, a free system cleanup utility that also includes a registry cleaning component. CCleaner found a full gigabyte of junk (temp files and fragments) to clean out, and though it doesn't indicate how much cleanup it is doing to the registry, I have no doubt there was a ton. The results: 2:36 until the OS was usable, but only 4:40 until non-stop hard drive activity ceased.

I then tried a registry-specific tool, Registry Mechanic (a $30 application). It identified 258 additional registry problems (many marked "severe"). After cleanup, again the OS popped up at 2:30, but the hard drive stopped cranking at 3:51.

These results are interesting: A clean registry doesn't have much effect until Windows is fairly fully loaded, but after that the performance improvement can be dramatic. I realize these figures represent just one measure of performance and just one machine, but if you're finding your computer is really slowing down, a registry cleaner might be able to help. Your mileage may vary.

Some caveats: A few people have complained that registry cleaning software made their system crash completely. This is always a risk with any software, but when you're messing around with the registry, you can far more easily break something. Remember to back up the registry before running a scanner, and tread lightly. If you're not comfortable restoring a registry file by running in safe mode and using regedit, you might want to get help before scanning.