When to upgrade: Tips for taking best advantage of Microsoft's release cycle

Computerworld - With the Vista operating system in beta trials and so many new products coming from Microsoft Corp., riding the wave of new technology may seem more like clutching onto the board than hanging 10 and surfing smoothly ashore.
Our clients have benefited from looking at Microsoft's release cycles in conjunction with their own. With some perspective, they can plan how to take advantage of new technology when it makes sense for their organization.
Operating System History
The Microsoft operating system release history definitely has a pattern. Client and server releases -- with several anomalies -- have happened roughly every three years and, generally, in the second half of the year.
Several factors have affected timing. For example, Microsoft's Trustworthy Computing Initiative added about 10 months to the release of Windows 2003 and Vista. Also, the three-year time frame represents two rotations of Moore's Law, which is enough to cause technology advances significant enough to require new hardware.
Other factors include branching and update releases. The first major branching took place with Windows Server 2000, followed by multiple products and variations of the operating system, such as Windows CE for Automotive and Windows XP Tablet Edition. Branching may affect the progression of major server releases as the complexity of maintaining the Windows code base increases.
Update releases are a new approach for Microsoft and effectively add a year to the previous three-year release cycle (see Microsoft's Windows Server Product Roadmap). These interim releases will happen two years after a major release. This new pattern offers customers more options to consider for their upgrade strategies and allows the operating system to stay more competitive during the new, longer major release cycle.
Calculate Cost Justification
You can use these trends to help determine how to maximize your company's return on the cycle variation you choose for the Microsoft operating system. Release cycles' relative predictability lets you calculate and capitalize on the operating system during the supported days on platform (SDP). The SDP represents the period during which patching and support are available from the vendor, as well as the period over which you can spread the fixed costs of installing the operating system. By calculating the cost and net gain generated by an operating system, you can estimate the value of adoption.
Costs associated with the operating system include installation and maintenance activities such as patching. In our experience, many of these costs are quantifiable, whether based on your company's historical expenditure or on analysts' estimates. You may have other costs specific to