In open source programming, version numbers or the terms stable and
unstable commonly distinguish the stage of development. The term stable
refers to a version of software that is substantially identical to a version
that has been through enough real-world testing to reasonably assume there are
no showstopper problems, or at least that any problems are known and documented.
On the other hand, the term unstable does not necessarily mean that there
are problems - rather, that enhancements or changes have been made to the
software that have not undergone rigorous testing and that more changes are
expected to be imminent. Users of such software are advised to use the stable
version if it meets their needs, and to only use the unstable version if
the new functionality is of interest that exceeds the risk that something might
simply not work right.
In the Linux kernel, version numbers are composed of three numbers, separated
by a period. Between versions 1.0.0 and 2.6.x, stable releases had an even
second number and unstable release an odd one. As of Linux 2.6.x, the even or
odd status of the second number no longer holds any significance. The practice
of using even and odd numbers to indicate the stability of a release has been
used by other open and closed source projects.
