How to Save More Disk Space with Compact OS on Windows 10

Kannon Yamada 30-03-2016

Compact OS is Microsoft’s newest take on handling factory resets. It decreases the operating system’s size using a combination of compression How Does File Compression Work? How does file compression work? Learn the basics of file compression and the difference between lossy versus lossless compression. Read More and software tricks. It also reduces the footprint of Windows apps.


If you’re on Windows 10, you can use Compact OS. Enabling or disabling Compact OS is easy, too. And it shouldn’t have any impact on your computer’s performance.

What Is Compact OS For?

Computers with vast amounts of storage don’t need Compact OS. It’s most suitable for 16 GB, 32 GB, and 64 GB eMMC modules or smaller SATA-attached Solid State Storage (SSD) devices. Implementing Compact OS frees around 1.5 GB (32-bit systems) or 2.6 GB (64-bit) of hard drive space (do you have a 64-bit Windows? Do I Have 32-Bit or 64-Bit Windows? Here's How to Tell How can you tell if the Windows version you are using is 32-bit or 64-bit? Use these methods and learn why it is important too. Read More ) and kills the recovery partition.

The biggest potential storage improvement is the elimination of the recovery partition. Nominally, the recovery takes up around 4 GB of space. But many laptop manufacturers include a recovery partition of their own, loaded with bloatware — in which case the recovery can create a much larger footprint.

For example, on my Dell XPS 13 Dell XPS 13 2015 Review and Giveaway The XPS represents the pinnacle of laptop design in 2015, and it's the best bang for your buck out of any laptop we've ever seen in the $800 price range. Read More , the recovery partition hovers around 7.3 GB in size. After enabling Compact OS, the total installed size of Windows 10 comes out to around 9 GB for the 32-bit version and 11 GB for the 64-bit version (what’s 64-bit and 32-bit?), which makes Windows completely usable on drives as small as 16 GB.

Compact OS changes all that by making even a 16 GB eMMC module usable. The tradeoff is that the OS requires more overhead whenever it draws on system files. But the impact is almost negligible. By the way, you can upgrade most 32-bit installations of Windows 10 How to Upgrade from 32-Bit to 64-Bit in Windows 10 Is your Windows 10 installation limited to 3.75 GB of RAM because it's the 32-bit version? We show you how to upgrade to 64-bit, so you can finally enjoy advanced features and performance. Read More to the 64-bit version for free.


compactos image microsoft

A non-obvious advantage of Compact OS is its impact on security: When performing a refresh or reset, Compact OS no longer restores files from the recovery partition. It instead loads patched files from within the Windows\WinSxS directory. Users will no longer need to download gigabytes of data following a reset. For those reselling a system, it saves a lot of time.

Here’s How to Get Started With Compact OS

First, open an elevated command prompt by typing CMD into Windows Search and then right-clicking on Command Prompt. From the context menu, select Run as administrator.

elevated command prompt windows 10


If you don’t have much hard drive space remaining, Compact OS could already be switched on. To find out, type in the command (Windows isn’t case-specific):

Compact /CompactOS:query

If the response states that the system is in the Compact state, then you are running Compact OS.

command prompt compactos query

To switch Compact OS on, type in the following command into an elevated command prompt:

Compact /CompactOS:always

Compression takes around five minutes on my Dell XPS 13. Do not shut your computer off while Windows compresses its system files.

To switch Compact OS off, type in the following command into an elevated command prompt:

Compact /CompactOS:never

Turning Compact OS on requires around five minutes to complete. Do not shut your computer off while Windows decompresses its system files.

Potential Risks of Compact OS

Power loss: The biggest potential risk is that you suffer a sudden loss of power while compressing or decompressing the Windows\WinSxS directory. If this occurs, it could potentially render the system unbootable and even unrecoverable. Windows might employ some safeties which provide protection, but the best option is to perform a complete backup 5 Basic Backup Facts Every Windows User Should Know We never tire to remind you to make backups and keep your data safe. If you're wondering what, how often, and where you should back up your files, we have straight forward answers. Read More before starting the process.


Performance loss: The second largest concern is that the operating system now requires a small amount of RAM when it accesses system files.

How Much of a Performance Loss?

Compact OS should only impact performance when the computer reads or writes to its system files or Windows apps. In this regard, apps should launch slightly more slowly. However, in my experience, the difference is entirely negligible. Apps feel just as responsive when compressed as when not compressed.

To prove that Compact OS doesn’t siphon much from the computer’s processing power, I benchmarked my Dell XPS 13, Broadwell edition, using PC Mark 8 (5 free benchmark programs The 10 Best Free Benchmark Programs for Windows Use these fantastic and free benchmark software for Windows to troubleshoot your system and keep it updated. Read More ), before and after enabling Compact OS. PC Mark 8 isn’t by any means an ideal solution, but its results suggest that Compact OS doesn’t hit performance much (or even at all).

PC Mark 8’s results indicate (perhaps erroneously) that my laptop runs faster with Compact OS enabled. I ran the benchmark several times and continued to experience higher benchmark scores with compression enabled.

uncompressed compactos benchmark

Is Compact OS Worth It?

For those of you who want between 1.5 and 2.6 GB of free space (plus the elimination of the 4 GB recovery), Compact OS is worth it. There is some concern that it may reduce functionality on systems with limited amounts of RAM, but on 4 GB, I noticed no performance loss whatsoever.

On the downside, Windows may not remove the recovery partition How to Restore a Deleted Recovery Partition in Windows 8 At the time, that extra storage space must have been very tempting. But now you need a recovery partition. We'll show you how to restore it. Read More . On my laptop, the recovery still resides on the hard drive, although it is no longer functional. The defunct recovery takes up 7.3 GB of space and requires third party software to remove it (such as EaseUS Manage Your Hard Disk Partitions Like A Pro With EaseUS Partition Master [Windows] When you ask a tech crowd about disk partition managers, many people will agree that EaseUS Partition Master is the best tools for the job. Why? Because it offers many great features, yet remains easy... Read More , AOMEI Partition Assistant, or Macrium Reflect Free). Be very careful if you remove the recovery and make sure to create a backup How to Create an ISO Image of Your Windows System Need to backup and restore Windows without backup tools? It's time to learn how to make an ISO image of your Windows PC. Read More before taking the plunge.

Has anyone else experimented with Compact OS? What were your results?

Related topics: File Compression, System Restore, Windows 10.

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  1. Jody Bruchon
    November 16, 2017 at 3:01 am

    You benchmarked performance on a Dell XPS but you mentioned that CompactOS is "most suitable for [small] eMMC SSDs." You did not benchmark the kind of machine that comes with such SSDs. Your XPS CPU is massively fast compared to the Celerons that usually come in cheap tiny laptops, so of course the compression will speed things up overall (decompression on that CPU is faster than disk access) but on a Celeron the situation will be reversed. Ironically, the bloated OEM recovery partition and OEM customizations more than justify doing a clean Windows 10 install immediately after purchase! On a 32GB eMMC SSD, a Dell Inspiron 11-3162 has about 9-10GB free out of the box; with a clean install of Windows 10 with no trash from the OEM, the free space almost doubles.

    It's also important to consider that CompactOS could affect performance even with a faster CPU because reading or writing any system file incurs a CPU load spike. One scenario where this could be disastrous for performance is with Windows 10's mandatory updates. If an update starts happening in the background, it's going to be writing a lot of compressed files which means significantly heavier CPU usage during the update process and slower updates.

    • Kannon Yamada
      November 17, 2017 at 2:33 am

      I also have a NuVision 8 with an Atom x5 and it doesn't appear to be slower with CompactOS enabled. I haven't done any serious testing, but CompactOS's overhead doesn't seem particularly severe -- even on low end devices.

    • Anon
      March 24, 2019 at 7:31 am

      There's some misunderstanding about compression, in fact, compression can improve performance in some workloads, especially for slow disks, caveats here are highly dependent on RAM space and CPU features. That's because often the OS will keep the uncompressed pages in memory rather than accessing the disk every time to uncompress a page, and compression algorithm in use trades off compression density to speed, and CPU features will negate performance penalties by speeding up certain instructions even on Celeron.

  2. Matt
    June 11, 2017 at 5:56 pm

    If the CPU / RAM overhead is insignificant, maybe it's gaining score from faster loading from disk, especially from a relatively slow laptop drive

  3. Anonymous
    March 31, 2016 at 1:28 pm

    This would also be great for M.2 SSD drives. :)

    • Kannon Yamada
      March 31, 2016 at 2:27 pm

      Good point, thanks Howard!