The Linux 2.6 kernel was released on December 17, 2003. A new major release of a Linux kernel is not an everyday occurrence: The last kernel, Linux 2.4, was released in January of 2001. This appendix lists features that are new to the 2.6 kernel.
Linux kernel revisions alternate between stable and unstable versions, so 2.4 was the previous stable version, and 2.5 was the development branch, which later became 2.6. For each of the major revisions, there is a series of minor revisions. Usually, minor revisions do not contain major changes, although one minor revision to the 2.4 kernel replaced the entire virtual memory subsystem, a major part of the kernel.
Fedora Core 2 and above include the 2.6 kernel. ...