At the time this tutorial was written, the most recent kernel available was 2.4.18. The 2.4.18 kernel is part of the 2.4 stable kernel series. This series of kernel releases is intended for production systems.

There are also several 2.5 series kernels available, but you should not use them on production systems. The "5" in "2.5" is an odd number, indicating that these kernels are experimental in nature and intended for kernel developers. When the "2.5" kernels are ready for production use, a "2.6" (even second number) series will begin.