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The microkernel story is full of good ideas and blind alleys. The story began with enthusiasm about he promised dramatic increase in flexibility, safety and modularity. But over the years, enthusiasm changed to disappointment because the first generation processor microkernels were insufficient and inflexible. Traditionally, the word kernel denotes the mandatory part of the operating system common to all other software. The kernel can use all features of a processor (e.g., programming the memory management unit); software running in user mode cannot execute such safety critical operations. Most early operating systems were implemented by means of large monolithic kernels. Loosely speaking, the complete operating system-scheduling, file system, networking, device drivers, memory management, paging, and more-was packed into a single kernel. In contrast, the microkernel approach involves minimizing the kernel and implementing servers outside the kernel. Ideally, the kernel implements only address spaces, interprocess communication and basic scheduling. INSETS: Frequently Asked Questions on External Pagers;Frequently Asked Questions on User-Level Device Drivers;Frequently Asked Questions on Memory Servers.

A security kernel is a software and hardware mechanism that enforces access controls within a computer system. The correctness of a security kernel on a PDP-11/45 is being proved. This paper describes the technique used to carry out the first step of the proof: validating a formal specification of the program with respect to axioms for a secure system. [ABSTRACT FROM AUTHOR]

An overview of the current and future positions with respect to operating system performance is given. While a great deal of information and a large number of models for subsystems have been developed, gaps still exist in our knowledge. Because of the severe interactions between the various subsystems of an operating system, an overall model of the total system must be developed to be able to analyze and design the performance aspects of an operating system. Although such total system designs are exceptional today, it is projected that they will become increasingly more common and necessary in the near future. Such a design philosophy will clearly have a severe impact on the way we go about modularizing operating and computer systems. [ABSTRACT FROM AUTHOR]