quite old news - but pretty interesting :)

Sources close to Microsoft confirm that The Beast is set to include a new relational file store at the core of its next version of Windows. Some roadmap slippage has apparently occurred, too, as the database core will be introduced into Longhorn, and Blackcomb has been pushed further back. That leaves a gap for a point revision of XP next year, although there's no sign of this on the roadmap just yet. Despite the annual revisions being named as users' number one bugbear, Microsoft hasn't let a year go by without releasing a new version of Windows since 1997, when it was fighting the browser wars.

more info on http://www.theregister.co.uk/content/4/23852.html