GMD--- German National Research Center for Information Technology
GMD SET--RS, 53754 Sankt Augustin, Germany
From a software-technology point of view, the-kernel concept is superior to large integrated kernels. On the other hand, it is widely believed that (a)-kernel based systems are inherently inefficient and (b) they are not sufficiently flexible. Contradictory to this belief, we show and support by documentary evidence that inefficiency and inflexibility of current-kernels is not inherited from the basic idea but mostly from overloading the kernel and/or from improper implementation. Based on functional reasons, we describe some concepts which must be implemented by a-kernel and illustrate their flexibility. Then, we analyze the performance critical points. We show what performance is achievable, that the efficiency is sufficient with respect to macro-kernels and why some published contradictory measurements are not evident. Furthermore, we describe some implementation techniques and illustrate why-kernels are inherently not portable, although they improve portability of the whole system.