Does Junk Data Slow Down Windows 10? Shocking Benchmark Results!

Helpful Windows PC Content from:
Does Junk Data Slow Down Windows 10

Like many good stories, this one also started on Reddit.

I signed up to Reddit a few days ago when Adam, the one who maintains and updates this website, told me that we should have a presence there. Why exactly, I don’t really know, but nevertheless, there I was.

If you don’t know, Reddit is a weird place. It’s the Internet’s truck stop where you can find almost anything.

There I was browsing for interesting discussions in Reddit when I stumbled upon a discussion at r/pcmasterrace/ where someone was asking for an alternative for CCleaner. The thread is here, in the case you want to see it:

reddit pcmasterrace junk data


I thought, well, this seems like a good topic to pop in and share my thoughts.

The discussion quickly escalated into a debate whether junk data, namely unneeded temporary files and unneeded registry data slows down your computer.

A Redditor claimed that no amount of temporary files or registry junk is going to slow down your computer.

His argument was that since leftover temporary files are not used by the operating system, they will not have any effect on the computer’s performance. No use, no harm, right?

That was an interesting argument and no one else seemed to doubt it, either.

And the argument makes sense.

However, I had a strong gut feeling that he was wrong.

I thought, surely, a large number of temp files and registry junk is going to slow down a computer. But it was, after all, only a gut feeling. An opinion. As an engineer, I don’t really work by gut feelings or opinions. I trust data.

Therefore, I designed a benchmark to answer one simple question: how much do temporary files and registry junk slow down a Windows PC?

My original hypothesis, which I also shared in Reddit, was that there needs to be a lot of junk data for it to have a measurable effect. I was thinking possibly million or so temporary files and perhaps even more registry data.

While on the surface the argument makes sense – that unused temporary file and registry junk is, by definition, unused and therefore no amount of such junk would slow the system down.

However, it’s not really true at all.

Even if Windows doesn’t use temporary files per se, Windows is still going to be in charge of updating the file system, for example. And while doing that, it is going to iterate through every single directory and every file, even if Windows doesn’t technically use such temporary files.

The same applies to the Windows registry. When your computer starts up, Windows is going to load up the entire registry, and iterate through all the registry data.

That is why I thought surely a large amount of junk data is going to slow your computer down.

Therefore, I designed a benchmark: A freshly installed, activated copy of Windows 10, fully updated as of the running of the test, that is, Wednesday, May 18th 2022. Only Firefox installed to the system.

Now, it’s not trivially easy to define what “slow your computer down” exactly means. One could be referring to the overall performance, such as the computer feeling sluggish, or some synthetic system benchmark results.

Or, as I think most of us could agree, a very easy and usable metric for a computer’s overall speed is how fast it turns on and allows the user to start to use the computer. Some theoretical benchmark result is one thing. How fast your computer starts up and is fully loaded and ready to use is another thing entirely. And that is what I focused on.

I used a stopwatch to measure three data points before and after the computer was filled with junk:

1) Time to desktop. How many seconds it takes for the desktop to load up?
2) Time to idle. How many seconds it takes for the computer to fully start up, in a way that the entire system is loaded? I define this by using the Windows Task Manager to see when the overall CPU usage drops to under 5%.
3) Time to open a website. How many seconds after the computer is fully started, it takes for Firefox to open’s front page and fully load and render it?

I would argue these three metrics are a fair way to establish how fast a computer is in everyday use.

Test one – before temporary files and registry junk added.

In the first test, I established the baseline. How fast does the computer run when its clean and without any junk?

Here are the results:

Time to desktop: 23 seconds.
Time to idle: 41 seconds.
Time to open a website: 57 seconds.

Windows 10 is very optimized to start up quickly. This is done by loading only the most important modules first and loading everything else on the background after the desktop has been shown to the user. This is why there is a noticeable delay from the “time to desktop” to “time to idle”.

Test two – the same computer filled with junk data.

To perform this benchmark, I used two scripts.

Firstly, I wrote a Windows batch file that creates 30 000 temporary files of three different types to three different temporary data folders in the system. That is a total of 270 000 files. Since we don’t want this test to be related to hard drive usage, each of the test files is small, about 8 bytes or less per file and therefore reading data from disk is not going to be the bottleneck.

Then, I created a registry import file that adds about 120 000 registry keys and entries to the Windows registry under a few different locations.

I’m offering both of these files for you to download so you can reproduce this test yourself, if you wish.

After the same Windows 10 system was filled with these temporary files and registry junk, I took the exact same measurements of the computer’s speed as before.

And it was shocking! The results are:

Time to desktop: 62 seconds.
Time to idle: 102 seconds.
Time to open a website: 118 seconds.

Having junk data caused the computer to take over twice the time to start!

Not only was the computer clearly slower, there were actual problems with the system: the Windows Task Manager was glitching with the Performance tab not seemingly working at all and the main process listing tab looking very unusual.

The system also felt sluggish. This feeling of being sluggish is of course impossible for me to objectively measure, but the system did feel slower, for example when simply trying to use the Windows Task Manager or launching Firefox.

I wanted to see how much temporary files and registry junk data slows down a modern, Windows 10 system. I was expecting to see some measurable effect but I was shocked how massive the effect was.

Having a lot of temporary files and registry junk clearly slows down your computer.

It’s worth noting that this benchmark is not about how much your typical computer system gets slowed down over time with the accumulation of junk data.

The point of this benchmark test was to address the original claim that no amount of junk files or registry junk data can slow down a modern Windows 10 based computer. And that, as my gut feeling told me, is absolutely incorrect. As we can clearly see from this test: too much junk data slows down your computer dramatically.

To show that I actually did this benchmark, I did it the way I describe it here and that the results are as I say, I performed the entire test while recording my screen. The video of this test being performed is published in our Youtube channel:

I’m also releasing the two script test files which I used to generate the test data. Feel free to use them to reproduce the test. You can download the script files from here:

The test was performed with VirtualBox 6.1 running on Linux Fedora 35 workstation host. The system is running on Intel Core i9-10900T CPU, 64 GB RAM, Nvidia Quadro P620 and Samsung SSD 980 Pro 2 TB hard drive. The virtual machine was dedicated with 2 CPU cores and 4 GB of RAM as recommended by VirtualBox.


Disclaimer: I’m the lead developer of jv16 PowerTools, Windows utility software whose one feature is cleaning Windows computers, including cleaning unused temporary files as well as registry junk. My username in Reddit is /u/JouniFlemming/ and we also have an official subreddit at /r/jv16powertools/ – Why not try out our application to see for yourself?

Computer Running Slowly?

For over 20 years, we’ve helped to keep Windows running smoothly.

When it comes to simple and effective PC maintenance, we’re trusted by Windows professionals the world over. Why not try for yourself and see the difference!  

Must Have Software

My computers are running 3 times faster than prior to using jv16 Powertools…

Rates a 20 on a scale of 1 to 10.


Trustpilot 5 Star Rating

Fix and Make Windows Faster