n the Internet. Consequently, people can rewrite the source code to rebuild the kernel, according to different requirements in various fields (Grace and Parker, 2000).
             Secondly,'the system libraries define a standard set of functions through which applications can interact with the kernel and that implement much of the operating-system functionality that does not need the full privileges of kernel code'(Silberschatz et al., 2003, p.701). Many types of functionality are provided by the system libraries, which allow applications to make kernel-system-service requests. Moreover, the libraries may also supply more complex versions of the basic system calls and routines that do not correspond to system calls at all, such as sorting algorithms, mathematical functions, and string manipulation routines (Silberschatz et al., 2003).
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