Kernel Version Numbering
All Linux kernel version numbers contain three numbers separated by periods (dots). The first number is the kernel version. We are now on the third kernel version, 2. Some of you may be running a version 1 kernel, and I am aware of at least one running version 0 kernel.
The second number is the kernel major number. Major numbers which are even numbers (0 is considered an even number) are said to be stable. That is, these kernels should not have any crippling bugs, as they have been fairly heavily tested. While some contain small bugs, they can usually be upgraded for hardware compatibility or to armor the kernel against system crackers. For example, kernel 2.0.30, shunned by some in favor of 2.0.29 because of reported bugs, contains several patches including one to protect against SYN denial of service attacks. The kernels with odd major numbers are developmental kernels. These have not been tested and often as not will break any software packages you may be running. Occasionally, one works well enough that it will be adopted by users needing the latest and greatest support before the next stable release. This is the exception rather than the rule, and it requires substantial changes to a system.
The last number is the minor number and is increased by one for each release. If you see kernel version 2.0.8, you know it's a kernel 2.0, stable kernel, and it is the ninth release (we begin counting with 0).