Windows Image Files (wim) is the file format used to deploy Windows operating system images that was introduced with Windows Vista. You will find two WIM files on all Windows installation media, located in the Sources folder:  boot.wim and install.wim.

The boot.wim file is the pre-installation environment (Windows PE) that is mounted during the initial Windows installation phase. Windows PE also functions as the Window Repair Environment (Windows RE), which can be used to perform startup repairs, memory tests and system restores.

The install.wim file is the image file that contains one or more image instances containing operating system files.

Both the boot and install image files can be customized to include additional updates, device drivers,  and applications using the set of tools freely available from Microsoft in the Windows Assessment and Deployment Kit (ADK) and the Microsoft Deployment Tool 2012.

These images are hardware agnostic which allows them to be used on any hardware, regardless of the specific hardware abstraction layer (HAL). The one exception to this is that you must use the x64 boot image to deploy x64 installation images.

WIM files may contain one or more deployable Windows images. You’ve probably experienced this during an installation of Windows 7 when the setup process asks you to choose a Windows 7 Edition. All of the files for each edition are stored within the image file. Despite that fact, the standard Windows 7 image file is only a little over 2 GB in size. This is because WIM files use a single-instance store process that only stores one copy of a file. When an image is added to a WIM file single-instance store checks the WIM file manifest to see if the file is already present. If the file exists in the WIM file, a pointer to that file location is made in the file resource for that image. This allows for the storage of several images within a WIM file without experiencing significant expansion of the file itself.

Since WIM files can contain several images, I recommend, as a best practice, to create one image file for each architecture type of each operating system. Below is an example:

           Windows Vista x64                  Windows 7 x64                Windows 8 x64

           Windows Vista x86                  Windows 7 x64                Windows 8 x64

Using your favorite imaging tool (ImageX, WDS, MDT2012) create your base images. Create your customized images that include the combination of drivers and applications needed and add them to the WIM file for the appropriate Windows version and architecture type.

Images in a WIM file are referenced using an index number, starting with the number 1. You can use the following ImageX syntax to discover the images and index numbers for each image in a WIM file.

                                                      Imagex /info [filename].wim

If you use Windows Deployment Services to deploy your images you won’t need the index number of an image, WDS will discover and display all images in a WIM file in the Install folder of the WDS console.

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