OSD “OS Install Packages” vs. “OS Images”
What’s the difference? Why two types? When should I use each?
These are frequent queries I get from customers and are also often echoed in the forums.
OS Install Packages are packages built using the actual source files from the OS media. For Windows XP/2003, this includes all of the individual files (in a compressed form) installed to a system during setup and the actual setup program. For Vista/7/2008, this includes an install.wim file that contains a generic “image” of the OS and the setup files used to deploy and configure this “image”. Note that WIM files are essentially just compressed archive files using the Microsoft CAB format; they contain the files that make up the OS and thus the Vista/7/2008 setup mainly just un-compresses the WIM onto the destination hard drive.
OS Images are WIM files without any other associated setup files. These are captured from a reference system that has been generalized using sysprep. The reference system is one where the OS has already been installed and possibly configured with software, updates, tweaks, and other configurations. This is all captured into the WIM file which can then be deployed to other systems making the two systems identical (minus any hardware difference of course).
Both of the above are stored in ConfigMgr packages. Package is a very ambiguous term though. For ConfigMgr, a package is a collection of source files contained in a specified folder and its subfolders; a package has no inherent functionality. Thus an “OS Install Package” has lots of files and an “OS Image” package has just one, a WIM.
OS Install Packages are used to deploy an OS from scratch using the OS setup program. In XP/2003 this means going through the “Blue Screen” setup. In Vista/7/2008 it means going through the PE based install.
OS Images are used to deploy a pre-configured OS built on a reference system (including any updates, software, tweaks, etc.). The advantage of using an OS Image is speed and the fact that it ensures that each system deployed is identical in configuration. Installing the OS and updates takes a long time typically as do some software packages. Capturing these in a single compressed file, like a WIM, eliminates the need to actually install any of these. An old Unix saying is that everything is a file. For Windows, not everything is represented as a file (as in Unix), but Windows is merely a collection of files – even the registry is just a set of files. Thus, deploying an OS contained in a WIM simply means extracting all of the files that the WIM contains onto the target system: full setup not needed.
OS Install Packages are directly used by Build & Capture Task Sequences to automatically create an image of a reference system captured in a WIM file. It is possible to use an OS Install Package to deploy systems; however, this is not commonly done — the trade-off is time as discussed above.
OS Images are used by Deployment Task Sequences to deploy an OS to target systems.
A common follow-on question is why not use the install.wim from the Vista/7/2008 media directly without creating a reference image first? The answer is because its not recommended: the install.wim for these OSes was built using the D drive as the OS root drive. The setup program goes through great pains to fix this after the install.wim is deployed. If you simply import the install.wim and use it in a deployment task sequence, you will have undefined results.
Thus, you should always build a WIM from reference system no matter what OS you are deploying. The preferred method is to use a build and capture task sequence, but manually building and capturing a reference system is “acceptable” although highly discouraged in my opinion.
A practice previously used by many when updating their images is to deploy an existing image, make changes, and then recapture the image. This is generally considered bad form for many reasons, but was technically acceptable. This is no longer the case in Vista/7/2008. A single installation of Windows is only allowed to be syspreped three times with these newer versions of Windows because of activation: http://support.microsoft.com/kb/929828. The best practice is always to create your images from a cleanly installed reference system; this is exactly what a Build & Capture Task Sequence does for you.