Abstract

The KeyKOS nanokernel is a capability-based object-oriented operating system that has been in production use since 1983. Its original implementation was motivated by the need to provide security, reliability, and 24-hour availability for applications on the Tymnet ® hosts. Requirements included the ability to run multiple instantiations of several operating systems on a single hardware system. KeyKOS was implemented on the System/370, and has since been ported to the 680x0 and 88x00 processor families. Implementations of EDX, RPS, VM, MVS, and UNIX have been constructed. The nanokernel is approximately 20,000 lines of C code, including capability, checkpoint, and virtual memory support. The nanokernel itself can run in less than 100 Kilobytes of memory. KeyKOS is characterized by a small set of powerful and highly optimized primitives that allow it to achieve performance competitive with the macrokernel operating systems that it replaces. Objects are exclusively invoked through protected capabilities, supporting high levels of security and intervals between failures in excess of one year. Messages between agents may contain both capabilities and data. Checkpoints at tunable intervals provide system-wide backup, fail-over support, and system restart times typically less than 30 seconds. In addition, a journaling mechanism provides support for high-performance transaction processing. On restart, all processes are restored to their exact state at the time of checkpoint, including registers and virtual memory. This paper describes the KeyKOS architecture, and the binary compatible UNIX implementation that it supports. 1.

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