Windows 10 Compact OS: Reducing the Disk Footprint

Windows 10 Compact OS: Reducing the Disk Footprint
Windows 10 has a new function allowing to reduce the disk space taken by the system.  The new function is called Compact OS and is an evolutionary development of WIMBoot technology implemented in Windows 8.1 Update 1. Compact OS allows to reduce the disk space occupied by the system due to compression of system files (like wim-file compression in WIMBoot). System files as well as preloaded Windows-applications files are compressed.
Compact OS allows to save around 1.5Gb disk space on 32-bit and about 2.6Gb on 64-bit Windows 10. The technology is intended first of all for owners of tablets, smartphones and laptops with low capacity SSDs.
After the compression, decompression file system is performed in memory on the fly, completely transparent to the system and applications. According to the Microsoft, Compact OS feature allows you to save disk space without a large drop in system performance.
Note Previously, we have described how to save the disk space in Windows 8 due to NTFS-compression of files in WinSxS directory. Details in the article: How to Clean Up and Compress WinSxS Folder in Windows 8
Compact OS can be activated both during the system installation and while operation. According to Microsoft’s documentation, the system determines whether Compact OS compression must be activated or not, depending on the system parameters (RAM size, processor performance and “other important factors”.) Compact OS will automatically be used in systems with low capacity SSDs (128Gb or less.)
You should understand that saving disk space using file compression reduces the system performance as it has to use additional processor and RAM resources to decompress the compressed files.
Let’s look at the Compact OS technology at work. So, there are 27.8Gb on the C:\ drive before the compression.
Windows 10 system compression
To know if system files are compressed using Compact OS,  run this command in the command prompt with the administrator privileges:
compact /compactos:query
If the utility detects that the current computer will not get any special advantages after using Compact OS mode, the system will return the following message:
The system is not in the Compact state because Windows has determined that, it is not beneficial for this system.
CompactOS - Windows 10
System file compression mode can be enabled manually regardless of the system assessment:
compact /CompactOs:always
Compressing OS binaries
Completed Compressing OS binaries
35401 files within 16674 directories were compressed.
5,309,743,895 total bytes of data are stored in 3,151,044,232 bytes.
The compression ratio is 1.7 to 1.
The compression will take some time, about 10-20 minutes. After the compression is over, compression ratio (1.7 times) and the value, by which the system files have been compressed, (in our example 5.3 GB were compressed to 3.1 GB) will be shown.
Thus, additional 2.71 Gb of the system disk space have become available.
additional free space
At first site, there are no problems with the loss of the system performance.
Compact OS mode can be disabled using the command:
compact /CompactOs:never
It is also worth to be noted that Windows 10 DISM utility got a new argument allowing to deploy the operating system with Compact OS mode enabled:
dism /Apply-Image /ImageFile:install.wim /Index:1 /ApplyDir:C:\ /compact

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