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Aboot image is a type ofdisk image that when on aboot device allows the associatedcomputer toboot.[1]
A boot image usually includes an operating system, utilities, diagnostics, boot and data recovery information and applications used organization-wide. A specialized image for a particular department or type of user may be called adepartmental boot image. Building such an image can take days or weeks, and involve complex decisions about licensing and permissions - including which passwords to store in the boot image and which to require users to type in - and requires experts insoftware integration to do.
However, once built, the boot image can be simply copied onto devices, patched within reasonable limits, and remains disposable in case of any problems (viruses in particular). This is possible because unlike other hard drive images (which may contain any data, et al.), pure boot images contain no mission-critical data. By definition a pure boot image contains no data that cannot be reproduced from configurations or off-the-shelf executables. In particular end-user data is not part of a boot image, although some operating systems require that a copy of user preferences or configuration files be kept within the boot image itself, e.g.Microsoft Windowsregistry. Utilities likeNorton Ghost keep a backup copy of the boot image, for quick re-imaging (often called re-installation) in the event of a problem, thus avoiding the need to diagnose a specific problem with a specific machine.
Somevirtual machine infrastructure can directly import and export aboot image for direct installation to "bare metal", i.e. a disk. This is the standard technique forOEMs to install identical copies of an operating system on many identical machines: The boot image is created as a virtual machine and then exported, or created on one disk and then copied via aboot image control infrastructure that also makesvirtual machine copies. TheVMware vCenter Converter for instance lets users "convert physical machines to virtual machines - for free"[2] as part of that company's suite of products to make images easier to back up and manage. Equivalents exist forXen and other VM systems.
By keeping the boot image entirely separate and disposable, and mandating boot image control, organizations seek to keep theirtotal cost of operations (including itstotal cost of ownership component) low. Often such organizations look atuptime as a service.
One goal of boot image control is to minimize the number of boot images used by an organization to reduce support costs. It includes at least:
Many organizations use thin clients for applications which require high security, involve unreliable users or repurpose older machines for continued use.
A cascading strategy involves re-imaging older, off-spec machines to thin client boot images so that they may continue in use for some less demanding or more access-controlled applications.