Compact OS, single-instancing, and image optimization

Windows 10 and Windows 11 have tools and features that help you save disk space and optimize your image.

Deployment tools that help save space

Windows 10 and Windows 11 include tools to help you use less drive space:

• Compact OS allows you to run the operating system from compressed files.
• Single-instancing helps you run your pre-loaded Windows desktop applications in compressed files.

Here's some ways to shrink the image, optimize the image, and some considerations when deploying to low-cost devices.

Compact OS

Compact OS installs the operating system files as compressed files. Compact OS is supported on both UEFI-based and BIOS-based devices. See the size comparison table below.

When running CompactOS, Windows update can replace or remove individual files as needed to help maintain the drive footprint size over time.

To deploy Compact OS using a WIM file

1. Boot your destination device with the Windows 10 or later version of Windows PE.

2. Create a pagefile equal to 256 MB.

   Wpeutil createpagefile C:\pagefile /size=256
   

   Where C is the Windows partition.

3. Format and prepare the partitions, and then apply the image to a partition using the DISM /Apply-Image /Compact option:

   DISM /Apply-Image /ImageFile:install.wim /Index:1 /ApplyDir:D:\ /compact
   

   This is usually done by running a deployment script. To learn more, see Apply Images Using DISM.

   Note

   If you're applying an image in compact mode and using the /ScratchDir option, make sure your ScratchDir folder is not on a FAT32-formatted partition. Using a FAT32 partition could result in unexpected reboots during OOBE.

To deploy Compact OS from Windows Setup

• Use an unattend.xml file with the setting: Microsoft-Windows-Setup\ImageInstall\OSImage\Compact. See Compact for more information.

Check if you're running Compact OS

You can query whether the operating system is running Compact OS, and change it at any time, using the Compact.exe command.

From Windows PE, determine if the OS is compacted:

Compact.exe /CompactOS:Query /WinDir:E:\Windows

Where E:\Windows is the folder where Windows has been installed.

From an online installation, change from non-compacted to compacted OS:

Compact.exe /CompactOS:always

Single-instancing of provisioning packages

when you add new Windows desktop applications to a device, you'll capture these changes into a compressed provisioning package for use by the automatic recovery tools. Rather than maintaining both the original files and the provisioning package, you can use DISM to remove the original files, and run from directly from the compressed provisioning package instead. This is known as single-instancing the image. See the size comparison table below.

While single-instancing is supported on both solid-state drives and rotational drives, for performance reasons, you should only use single-instancing on devices with solid-state drives.

Example:

DISM /Apply-CustomDataImage /CustomDataImage:C:\Recovery\Customizations\USMT.ppkg /ImagePath:C:\ /SingleInstance

where C:\ is the drive letter of the Windows partition.

You can determine whether a provisioning package (.ppkg) is single-instanced by using fsutil.exe:

fsutil.exe wim enumwims C:

where C is the drive that contains the provisioning package. Any single-instanced provisioning package on the drive will be listed in the command output. If there are none, the command will return "Error: The system cannot find the file specified."

Image optimization

After applying updates to a Windows image, cleanup the image and then export it to a new file:

md c:\mount\Windows
md C:\mount\temp

Dism /Mount-Image /ImageFile:"C:\Images\install.wim" /Index:1 /MountDir:C:\mount\Windows

Dism /Cleanup-Image /Image=C:\mount\Windows /StartComponentCleanup /ResetBase /ScratchDir:C:\mount\temp

Dism /Unmount-Image /MountDir:C:\mount\Windows /Commit

Dism /Export-Image /SourceImageFile:C:\Images\install.wim /SourceIndex:1 /DestinationImageFile:C:\Images\install_cleaned.wim

where C:\Images\install.wim is a Windows image file that you want to update. You can optionally specify the /Defer parameter with /ResetBase to defer any long-running cleanup operations to the next automatic maintenance, but you should only use /Defer as an option in the factory where DISM /ResetBase requires more than 30 minutes to complete.

Size requirements and considerations

You'll still need to meet minimum size requirements for the hard drive, RAM, application resource usage, and data storage.

Hard Drive

Although some configurations of Windows may appear to fit on smaller drives when Windows is first installed, 8 GB SSDs are not large enough. Even if a user pairs an 8 GB hard drive with a second drive that is 4 GB or larger for application and data file storage, 8 GB hard drives do not allow for the increase in the Windows memory footprint that is expected to occur as users work on their computer.

Some of the primary reasons for the increase over time in the memory footprint include the following:

• Servicing. Hard disk space must be reserved for applying update packages to the operating system.

• System Restore Points. Windows automatically generate restore points. The amount of space that is required by default is relative to the size of the hard drive. For more information about restore points, see the Restore Points topic on MSDN. Note   Users can adjust the amount of space used on the computer for System Restore by using the System Protection user interface in the System Properties dialog box (Sysdm.cpl). Users can also use system image backups that are stored on an external hard disk to restore a system.

• Logs and Caches. The operating system stores files such as event logs and error logs on the drive.

RAM, Pagefile.sys, and Hiberfil.sys

The Pagefile.sys and Hiberfil.sys files increase in size in direct proportion to the amount of RAM on the computer. Windows installations on 16 GB drives have a smaller memory footprint when the computer is limited to 1 GB of RAM. An increase of RAM to a size that is greater than 1 GB will result in increased size of the system files and less space on the hard drive for other applications and files. Increasing the size of the hard drive, however, does not affect the size of these system files. Learn more about On/Off Transition Performance

To save space on the drive, you can remove or reduce the size of the hiberfil.sys. See the size comparison table below. To learn more, see Lab 7: Change settings, enter product keys, and run scripts with an answer file (unattend.xml).

• powercfg /h /type reduced : Reduces the file by 30%
• powercfg /h off : Removes the file.

Language packs and features on demand

Installed language packs (LPs) can take more space than just the size of the LP itself. When you preinstall FODs and UWP apps on a Windows installation that contains multiple LPs, resource files based on preinstalled LPs are also installed. When unused languages are automatically removed after OOBE, corresponding UWP and feature on demand (FOD) resource files are not removed. Preinstalling fewer LPs saves disk space by limiting the number of resource files that remain on a system after removing unused language packs.

Features on demand are distributed in compressed CAB files so the size of an installed FOD is larger than the size of the original CAB. You can use /Get-CapabilityInfo in DISM to view an FOD's download and install sizes. See Features on demand for how to get information about FODs.

Windows optional features

In order to further save disk space on a Windows device, you can disable various optional features that may not be in use.

Through DISM or PowerShell, you can enable or disable Windows optional features as needed.

Applications

Software applications that are installed on the computer may require additional space for caches, logs, and updates. Disk space must also be available on the drive to account for temporary increases in resource usage during installation of applications, patches, and updates.

User Data

On computers that support removable media such as an SD card or USB flash drive, users can easily expand personal data file storage for user documents by using this removable media. However, we recommend that users reserve some space on the hard drive for these types of files.

Size comparisons

The table below shows the additional space saved by using compact OS, Single instancing, and reducing or turning Off Hiberfile on 2GB (x86 processor architecture) and 4GB (x64 processor architecture), on Windows 10, version 1607:

Related topics

Capture and Apply Windows, System, and Recovery Partitions

DISM Image Management Command-Line Options