Microsoft has extended mainstream support for Windows Server 2008 by 18 months.

Announced in the latest Microsoft Support Lifecycle newsletter, the extension was triggered by a company policy that requires an extension if the follow-up product is slow to arrive, among other reasons.

"The Microsoft policy provides a minimum of five years of Mainstream Support or two years of Mainstream Support after the successor product ships, whichever is longer," the newsletter said (emphasis in original).

Microsoft considers the true successor to Server 2008 to be Server 2012, which debuted last month. The September debut pushed the end of mainstream support for Server 2008 from July 9, 2013, to Jan. 13, 2015. The end of extended support for Server 2008 is now Jan. 14, 2020.

In mainstream support, Microsoft offers security patches, general fixes and feature updates free of charge. During extended support, which runs five years beyond mainstream support, it offers free security updates only but will provide non-security-related bug fixes for a price.

Support extensions are not unprecedented. Microsoft recently prolonged support for the consumer versions of Windows 7 and Windows Vista by five years to sync them with the enterprise editions' life spans.