The fact that the Windows Vista install DVD is just one big pre-installed system image makes it surprisingly easy to build your own disc with patches, drivers and even applications pre-installed.
The bottom is about to fall out of the market for imaging tools like Symantec Ghost: Windows Vista is based entirely around Microsoft's own system imaging technology. The Vista install DVD is, in fact, just one big system image.
In the XP world, most advanced users are used to customising the Windows install disc. It's a straightforward, if tedious, process to slipstream service packs and patches, add extra drivers and create answer files that allow XP to install with no user input.
But this flexibility only extends to the installation of Windows itself. To clone a full system with apps installed, Symantec Ghost or a similar utility must be used to create that image.
However, all this is about to change. Windows Vista is based entirely around Microsoft’s Windows Imaging Format (or WIM), a file-based imaging standard rather than a sector-based. this means that the image isn't a bit-for-bit image of your disk layout, and hence you can apply the image to a new system without destroying the contents of the hard drive.
Also, Vista is hardware-agnostic, so you can use a single system image as a source for multiple hardware platforms, even if they have quite different hardware configurations.
Being file-based also enables certain features which will prove seriously useful. When capturing a system to a WIM file you can specify exclusions. For example, you can have a work directory on the system with temporary data. Instead of having to clean it up every time you can simply exclude it from the capture. The same applies to session-based files like the pagefile - it will be recreated when the system boots anyway, so why waste space?
Single-instance files are another advancement. WIM files can store more than one image, so you can have multiple system configurations stored within the one WIM, but to avoid image bloat single instancing checks each file referenced in each image. When more than one image references the same file (for example, almost the entire contents of the C:\Windows directory), the physical file is only stored once within the WIM and every image which references it is directed to that copy. Each file stored in a WIM is assigned a unique SHA-1 hash, so version integrity is assured.
Interestingly you can have as many images contained within one WIM file as you think you can manage, and any one of them can be marked as bootable.
All WIM images feature one of two compression technologies - LZX or XPress. LZX gives greater compression when space restrictions are an issue, and is the option of choice when installing from fast media like a DVD.
For CD/DVD-based installs, WIMs can be split into multiple SWM files for media spanning. XPress is a faster compression algorithm, and gives the best performance when deploying the image across a network.
Compression along with the single-instancing means that WIM-based images will offer major space-saving benefits over traditional imaging formats like Ghost. Of course, it’s not an all-in-one imaging solution. It’s still dependent on delivery systems like SETUP.EXE, SMS (Systems Management Server) or WDS (Windows Deployment Services - the successor to RIS, Remote Installation Services). But that’s no different from any other imaging system.
In the next blog update I’ll go through the Microsoft tools available to interact with and customise WIM images - it’s seriously cool stuff!
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