But sometimes, even numbers = stable release, one that is fit for production use. Odd numbers = development release, for testing potentially unstable new features and drivers. "Prior to the Linux 2.6.x series, even numbers indicate a stable release, i.e. one that is deemed fit for production use, such as 1.2, 2.4 or 2.6. Odd numbers have historically been development releases, such as 1.1 or 2.5. They were for testing new features and drivers until they became sufficiently stable to be included in a stable release." -Wikipedia