Windows has a compression mode that Microsoft never mentioned and it gave me 38GB on the C: drive.

Whether it’s a multi-terabyte Gen 5 NVMe or a 500GB SATA SSD, everyone wants a little more space on their drive. If you can’t afford to buy more, the next best thing is to soften your drive as much as possible by freeing up space for the apps and services you use.

Many third-party utilities offer a deep clean of your computer and reclaim gigabytes of storage, and of course, some of them may do so once they have your credit card details and email address. But if you’re on Windows 11, the tool to do it is already on your device, and Microsoft barely mentioned it. Here is the built-in operating system compression mode works and what it gave me.

Windows has a compression mode that is never in front of you

It can run the entire operating system from compressed files and save some storage space

The first thing you need to know Small OS it’s not a once-a-month cleaning trick or cache-cleaning method. This is a mode that saves individual Windows system files as compressed files and starts the OS directly from them, so Windows itself is smaller on your disk. Microsoft did this for devices with smaller SSDs, where every gigabyte stored on the C: drive counts, but anyone with any SSD can save some storage space with this method.

This way of working is very simple to understand. After compression is applied via a simple command-line script, Windows opens each file as it’s read, so all your apps, games, and services behave exactly as they did before.

One thing to be aware of is that, like all forms of compression and decompression, it costs CPU cycles. Every time a compressed file is downloaded, your processor must decompress it, so Microsoft reserves this feature for machines that need space rather than enabling it by default. You’ll never feel it on anything with a modern processor and a fast NVMe SSD.

The most interesting thing is that the tool is not limited to Windows. Compact OS is a variant of the built-in compact command, and you can point that command to your own folder (such as the game installation or applications directory) to compress it in the same way.

How to use Windows 11 compression mode?

Adding it takes one command and about 5 minutes

Everything about this approach is done in an elevated terminal, so you can open PowerShell or Command Prompt as an administrator to get started. Before entering commands, it is always a good idea to check what state your operating system is in, which can be done with the following command:

compact /compactos:query

On two of my machines (including a desktop with a PCIe Gen 4 NVMe SSD and a Lenovo Legion 5 Pro), it indicated that the system was not in a compact state because Windows decided it wasn’t useful, which is the default on any setup with free space. The feature works the same way when Windows looks at your drive and decides you don’t need the extra space. You can override this decision.

Before you can easily determine how much space the process has freed up for you, I recommend checking the free space afterwards. You can do this in the following ways:

Get-PSDrive -Name C

This will give you a screenshot of the C: drive detailing the free and used memory. With this image in mind, you’re ready to apply compression with the following command:

compact /compactos:always

Now all you have to do is wait. There will be no progress bar and the window will be “compressing OS binaries” for a while. On my Legion 5 Pro laptop, the process finished in five minutes, and when it was done, it printed a summary with the compression ratio and the number of files compressed. you can run Get-PSDrive – Name C run the command a second time, and the difference is the space you just recovered.

I’ve tried this method twice, once on my Legion 5 Pro and once on my desktop. With Compact OS alone, the free space was around 7GB on the laptop and 5GB on the desktop. But you can go further than that, I got back about 40GB of storage on my laptop.

How I recovered 38 GB with compression

All that was needed was to point to the correct folder

Compact OS itself only touches Windows’ own files, so after doing this, I curiously pointed that compact command to the folder of my choice. Users folder on the laptop.

compact /c /s:"C:\Users" /exe:lzx /i

LZX is the strongest of the compression algorithms available, /s applies it to every file in the folder and /i tells it to continue with anything it doesn’t touch instead of stopping. This method is not as fast as Compact OS and took about thirty minutes in total to scan thousands of files.

When it was done, the summary said it had gone through 460,000 files and bought 190GB of data down to 158GB, a saving of about 31.5GB. With the 7GB the Compact OS reclaimed, my laptop had 38GB more free than when I started that evening.

I’ve experimented enough to know where it doesn’t work. I also tried to point it to my Xbox Games folder, hoping to free up some space, but nothing came back. This is probably because games send their assets to already compressed archives.

Are there any negotiations? And is this process reversible?

These were two questions I immediately asked myself before attempting to do this on my main desktop. The answer to both questions is yes. It takes CPU cycles to decompress each compressed file, so it’s disabled by default on most machines. It doesn’t affect me on a Ryzen 7000 series CPU and Gen 4 NVMe, and it probably won’t affect you if you’re on similar hardware.

As for reversing it, it’s plain and simple. To uninstall Compact OS, you can run the following command:

compact /compactos:never

To do this for any folder you’ve zipped:

compact /u /s: "C:\(FOLDER NAME)" /exe /i

For all these reasons, it’s worth a try if you’re looking to save space on a device with limited storage. The way it works is that you never have to delete anything and free up a decent chunk of memory, making it one of my favorite disk cleanup methods.