The latest update of Windows 8.1 brings an interesting functionality which allows to use lower end machines with small SSDs save space so If you have such a PC or tablet which has a small SSD and struggling to get everything installed, you might consider this type of installation. It's called Windows Image Boot (or WIMBoot) and allows to organize the disk partitions different way by keeping the WIM installation file in separate partition without uncompressing and copying the system files to the C: drive. WIMBoot in Windows 8.1 uses the restoration partition containing the recovery WIM image as target for booting the system. Some sites reports as well that it's possible to run on systems with RAM as low as 1 Gb.
The main benefit is for systems with small capacity SSDs, like tablets. As an example for a device which has only 16Gb SSD you would traditionally use 9Gb and had left 7Gb of free space after installation (and only if not setting up a recovery image. Otherwise you'll lose even more space) whether with installing Windows 8.1 by using VIMBoot configuration you would use only 3Gb and had left 12 Gb of free space. And the recovery image (a way to recover by booting a clean environment.
WIMBoot in Windows 8.1 – How does it work?
The WIM file gets copied to a separate partition and from C: there is a pointer which points into the WIM file. Windows is aware of the compressed WIM file and allows to boot from there. All the files are kept in the WIM. The user profile, apps, Windows updates, and anything else applied to the OS after it is initially installed will be in the “real” C: drive (Note that the WIM is read-only).
The whole disk with all the partitions looks like this. Img. from Microsoft blog:
The traditional approach will otherwise partition the drive like this:
Quote from Microsoft:
Effectively, you copy the WIM file into a separate “images” partition (just like you would for a recovery image), then use DISM to create pointer files from the standard C: operating system volume into the WIM file. These pointer files are completely transparent, and Windows knows how to boot the operating system (keeping all the files in the WIM) when configured in this setup.
The downside is that it that the compressed image might cause a little bit of performance loss.
WIMBoot in Windows 8.1 limitations:
- WIMBoot is available for client editions of Windows 8.1 with Windows 8.1 Update only (not server versions). All architectures are supported, including amd64, x86, and ARM. Some enterprise deployment tools do not support WIMBoot.
- WIMBoot is available only for UEFI-based PCs running in UEFI mode (legacy BIOS-compatibility mode isn't supported).
- WIMBoot is supported for solid-state drives and eMMC (Windows HCK compliant) drives. WIMBoot isn't supported on traditional drives that contain rotational components, or on hybrid drives that contain both solid-state and rotational drive components. WIMBoot works by taking advantage of the capability of solid-state drives to access different areas of the hard drive quickly.
It's OK to have a secondary drive attached to the PC, and the secondary drive can contain rotational components. But the WIMBoot image and pointer files must all be located on the primary solid-state or eMMC drive. - Some backup, antivirus, and encryption tools aren’t compatible with WIMBoot images.
You can check how to proceed on Microsoft Technet here where you also find a script which used Diskpart, but basically you must first partition the drive in 4 partitions – for System, MSR, Windows and Images. The WIMboot is part of Microsoft ADK for Windows 8.1 – check the details here.
