Many organizations are still running applications based on legacy operating systems, and there are several reasons why these organizations would prefer to continue to use them. Some may have deployed custom software for which the source code, programmers, or documentation are no longer accessible, making the effort of upgrading to current operating system versions difficult, costly, or time consuming. Some may have deployed commercial software, and are reluctant to undertake the effort and expense to license newer versions of the application and corresponding operating system software. And some may run commercial software for which there is no updated version.

Regardless of the reasons for staying with an older generation of operating systems, there are numerous reasons why the same organizations are motivated to upgrade the servers on which their older applications run:

• Hardware that was deployed years ago to support the applications is at the end of its useful life, with service contracts expiring, and the incidence of faults increasing.
• After years of keeping up with demands to constantly deploy new applications, datacenter space is scarce, leaving Information Technology (IT) organizations to find ways to deliver the same applications in the same space, using less power, and with less cooling expense. Older servers are less efficient by all measures.
• Old applications may need newer peripherals including Storage Area Network (SAN)-based storage systems, backup devices, and high-speed network interfaces.
• The CPU performance and memory capacity of older servers is severely limited, making it difficult to increase application throughput to support newer, larger workloads.