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WIMBoot Is the Secret to Leaner Win8.1 Update Installs

In spelunking around on TechNet, I’ve come across an interesting element in the latest Windows Assessment and Deployment Kit (ADK). It’s called WIMBoot and it appears to explain quite nicely how it is that Microsoft has been able to trim down the size of Windows 8.1 Update 1 installations. In fact MS has a pair of interesting illustrations that *show* how this works, and an explanation as to why a smaller image and runtime environments result. The image pair is best understood as a kind of “before” and “after” scenario, in light of this explanation from the WIMBoot Overview (taken verbatim from its “How does it work?” section):

In a standard Windows installation (without WIMBoot), every file is written to disk at least twice: once in the compressed form for recovery, and once in the uncompressed form in the applied image. When the push-button reset feature is included, the compressed image remains on the PC. Having both the Windows installation and recovery image on the device can take up a lot of disk space.

When installing Windows with WIMBoot, you write the files to the disk only once, in compressed format. Next, you apply a set of pointer files onto the Windows partition that point back to the compressed files in the Images partition. When the user adds files, apps, or updates, they’re added onto the Windows partition.

In WIMBoot, your WIMBoot image is also used as the recovery image, saving disk space.

Here are the symbolic (not-to-scale) disk layouts for the before and after scenarios:

The Standard partition layout includes MSR, WinRE, uncompressed Windows files, and a Recovery partition.

The WimBoot partition layout drops WinRE, keeps Windows files compressed, and stores install.wim, winre.wim, and custom.wim.

Overall savings on disk footprint can be pretty substantial, with reductions in size of 6 GB or greater typical. This is essential for smaller configurations, particularly for tablets with 32 GB of storage space or less, but it could also be nice for tablets, ultrabooks, or notebooks where storage space may still be at a premium. For more information on how to set up and build such installations, see also the following TechNet elements:

1. Create WIMBoot images
2. Deploy WIMBoot Images: If you know the size of the images upfront (explains “push-button reset tools” and includes a pointer on how to Update WinPE5.0 to WinPE5.1)
3. Deploy WIMBoot Images: If you don’t know the size of the images upfront
4. WIMBoot: Identify if your PC is Configured to Boot from a WIM file

I can’t wait to try this out, and see how it goes. I also plan to contact my buddies as Paragon Software to see if they might not be working on some tools to help automate this process. If you know of other tool providers with similar work underway, please drop me an e-mail.

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