Operating Systems: Concurrent and Distributed Software Design

26.4. Downloadable code

In Section 26.3 we examined microkernels and the Mach system in particular. These systems provided OS functions from a number of communicating user-mode server processes. Microkernels enable a great deal of flexibility in the policies implemented by components of the system and, if designed carefully, allow components to fail and be restarted without interrupting the system as a whole. However, it is interesting to examine the trade-offs that exist between this level of flexibility and the costs of the IPC mechanisms that are required to support it. An alternative mechanism for extensibility, downloadable code, takes a very different approach to integrating new functionality with the running OS kernel by allowing sections ...