The newly released Windows 10 introduced a new feature called Compact OS. This technology is the evolution of WIMBoot in Windows 8.1. In short, the Compact OS allow the system files compressed like wim file and transparent to the upper level in order to reduce the size of the system files for more free space.
However, the installation/upgrade program would automatically decide if the current system should use compact OS deployment or not. According to the Microsoft, the RAM size, CPU speed and “other important factors” would be evaluated to make this choice. As for the details or the extract evaluation standard? Unknown. Only one thing for sure, Compact OS would only be enabled on SSD if needed by system, as it was for the WIMBoot. So if your Windows 10 was deployed on a HDD, this post may not work for you.
After some testing, I found that the system disk size (not only the OS partition like C:\) may be the main factor for the compact OS policy.
Test machine 1: Intel i7 – 4770K + 16G RAM + 128G SATA3 SSD(118G for C:\) -> Compact OS enabled by default.
Test machine 2: Intel i7 – 4770K + 16G RAM + 256G SATA3 SSD(237G for C:\) -> Compact OS disabled by default.
Test machine 3: Intel Core 2 T9900 + 8G RAM + 480G SATA2 SSD(80G for C:\) -> Compact OS disabled by default.
Test machine 4: Intel Atom N450 + 2G DDR2 RAM + 64G SATA2 SSD -> Compact OS enabled by default.
Although the Compact OS can greatly reduce the size of the OS files, it is still not beneficial for devices which CPU speed is the bottleneck, as well as the devices equipped with quite limited RAM.
To check the current status of the Compact OS, simply use the following command in Command Prompt or Windows Powershell:
> compact /CompactOs:query
If the system decided that current machine cannot gain the benefits by enabling Compact OS:
You can also enable it manually regardless the system decision:
> compact /CompactOs:always
The compress ratio using the default algorithm could be around 1.6 to 1.
Don’t want any of these Compact OS stuff?
> compact /CompactOs:never
Besides, Unlike the WIMBoot, the manual deployment of the Compact OS is quite easy. A “/compact” argument was added to the dism program to do the job:
> dism /Apply-Image /ImageFile:install.wim /Index:1 /ApplyDir:C:\ /compact
References:
How Windows 10 achieves its compact footprint
Compact OS, single-instancing, and image optimization