Boot image control

A boot image control strategy is a common way to reduce total cost of ownership in organizations with large numbers of similar computers being used by users with common needs, e.g. a large corporation or government agency. This is considered part of enterprise application integration in larger shops that use that term since applications are part of the boot image, and modify the boot image, in most desktop OS.
Windows Vista includes tools for boot image control, displacing third party tools. Mac OS has always had more flexible handling of boot drives, simplifying control and reducing the need to move boot images around between drives. Increasingly, boot image control is a network operating system function. 
Economics.
Very often a large computer vendor is required to explain in a bid in response to an RFP how they intend to simplify the purchaser's boot image control problems and the attendant service costs:
The total cost of ownership correlates strongly to the total number of different images, not the total number of computers, so this is a major cost concern. Three basic strategies are commonly advised:
Thin client strategies.
Organizations that do not closely track, control and set common standards for, acquisition of new computer hardware, typically can only practice a thin client strategy.
Which strategy will reduce total cost of operations the most depends on several factors:
More complex departmental boot images.
While the departmental boot image strategy seems to be the most flexible, the complexity of creating and managing several large boot images, and determining when a department needs to upgrade its applications, can easily outweigh these. Especially if users object and try to subvert the discipline of waiting for a regular boot turn to upgrade all machines at once. If each user is allowed to do this on their own, then, the discipline soon degrades into effectively a bunch of home computer whose issues are not really diagnosable nor comparable to each other. In which situation thin clients may become the only practical answer:
Many organizations use thin clients for applications which require high security, involve unreliable users or repurpose older machines for continued use. This much simplifies boot image control by facilitating centralized management of computers, and has many advantages:
While control of the images is simpler, there are disadvantages. Thin clients:
Many organizations try to gain the advantages of thin clients without the disadvantages by treating many very standard machines as if they were terminals, but with very much greater capabilities. As they buy new computers, they put the demanding applications on those.
Boot turns and re-imaging.
Administrators perform a regular (often bi-annual) boot turn that re-images many older, off-spec machines at once so that new hardware can be deployed for higher-end use. This procedure is called cascading: the oldest hardware is repurposed with simpler software to let it continue in use for some less demanding or more access-controlled applications, but subjects it to much more rigorous control to minimize the number of images.
The total cost of operations correlates strongly to the total number of different images, not the total number of computers. To minimize the number of images requires additional discipline:
Open configuration and semantic services.
Desktop computing is increasingly relying on web services, making the thin client approach more viable. Departmental boot images may remain but simply instantiate part of a semantic service-oriented architecture, especially in larger organizations. A service component architecture would further simplify the implementation of control mechanisms, especially if a single application language like Java was used for all custom applications in the enterprise. More importantly, shift to software as a service by most large vendors means that applications are not tied to machines, so the number of variant boot images required (with the applications installed) is reduced.
Other open configuration technologies such as Bitfrost, OpenID and even XMPP would also simplify configuration of boot images, as authentication would no longer be dealt with on the desktop/laptop device.
Vendor support.
Large system vendors increasingly provide DVDs with the boot image standard for the machine as shipped to the customer, which usually includes tools to diagnose changes to the machine and download drivers.