Linux distinguishes stable kernels from development kernels through a simple numbering scheme. Each version is characterized by three numbers, separated by periods. The first two numbers are used to identify the version; the third number identifies the release.
As shown in Figure 1-1, if the second number is even, it denotes a stable kernel; otherwise, it denotes a development kernel. At the time of this writing, the current stable version of the Linux kernel is 2.4.18, and the current development version is 2.5.22. The 2.4 kernel — which is the basis for this book — was first released in January 2001 and differs considerably from the 2.2 kernel, particularly with respect to memory management. Work on the 2.5 development version started in November 2001.
Figure 1-1. Numbering Linux versions
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New releases of a stable version come out mostly to fix bugs reported by users. The main algorithms and data structures used to implement the kernel are left unchanged. 15!
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