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It seems that Windows gets bigger with every release. This hasn’t been an issue with most devices because storage is so incredibly cheap. Certain devices could benefit from more storage, though. Getting more storage can involve cloud-based solutions and creative tweaks to the OS. Windows 8.1 Update brought a new method by modifying the deployment procedure. This installation is called WIMBoot.
What is WIMBoot and why should I care? ^
A normal Windows 8.1 install, fully patched, comes in just shy of 10 GB. The same machine configured for WIMBoot would weigh in at just over 3 GB of used space. That is quite a bit of space savings! WIMBoot has two other benefits. The first benefit is that Windows will deploy faster, as you do not have to extract the setup files as often. The second benefit is that your refreshing/restoring procedures will complete more quickly.
WIMBoot does have a few limitations. It is only supported on Windows 8.1 Update. The architecture doesn’t matter, however; WIMBoot can be used on standard x86 and x64 setups and can even be used on ARM machines like the Surface 2.
WIMBoot has two hardware requirements. The device must support UEFI, and the OS has to be installed on a solid state drive. If you have a new machine that supports these requirements, you can see if your OS is booting from a WIM file. Launch Disk Management and select your primary boot drive. As seen in the screenshot below, machines using WIMBoot will be labeled as such.
Disk management for a WIMBoot and a non-WIMBoot machine
How does WIMBoot work? ^
At WIMBoot’s core is a completely new partition layout. Microsoft has detailed the partition layouts here. As you can see in the screenshot below, the Windows Recovery partition no longer exists independently in a WIMBoot setup.
Comparing a standard install to a WIMBoot install
You will also notice a completely different structure in the standard Windows partition. Normal setups contain two copies of every default file. Compressed copies are stored for recovery. The uncompressed files are stored in the Windows partition (for example, C:\Windows).
A WIMBoot setup still has the first set of compressed files, which are stored in the Images section. What differs is that pointer files are used in the Windows partition instead of uncompressed items. When a file is needed, a pointer file connects the content to the compressed WIM. This method of access is slower than the traditional uncompressed method, but this is what makes the space savings so significant. By requiring an installation on a SSD, a user shouldn’t notice the performance difference. Files added by the user (documents, apps, etc.) are added directly to the Windows partition.
What are the limitations of WIMBoot? ^
As a technology, WIMBoot is still in its infancy. Most deployment methods will not support a WIMBoot deployment method without a few workarounds. MDT 2013 can deploy WIMBoot in an experimental task sequence. The process involves editing some of the MDT task sequence scripts. Full instructions can be found here. If you are preparing your WIMBoot image manually, you will need the Windows 8.1 Update for the ADK tool set. The steps for manual creation of a WIMBoot image can be found on TechNet.
Because disk performance with WIMBoot is slower, certain security software might have issues. The use of BitLocker, for example, is strongly discouraged. Microsoft also states that some backup and antivirus tools might be incompatible with WIMBoot.
Regardless of issues and limitations, WIMBoot remains a very promising technology. It can allow for cheaper devices to run Windows, and it can save money by enabling IT departments to purchase smaller SSDs in their devices.