Applications often require functionality that is implemented in the kernel, but is not directly available to the user level. While extensible operating systems allow kernel functionality to be augmented, we believe that the emphasis on extensibility is misplaced. Applications should be able to reuse kernel code directly and the emphasis should be placed on designing a kernel with that reuse in mind. The advantage of structuring the kernel as a set of reusable, extensible tools is that applications can avoid re-implementing functionality that is already present in the kernel. This will lead to smaller applications, fewer lines of total code, and a more unified computing environment that will be easier to maintain and perform better.
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