We have implemented a default memory manager for the Mach 3.0 kernel that resides entirely in user space. The default memory manager uses a small set of kernel privileges to lock itself into memory, preventing deadlocks against other Mach systems services. An extension to the Mach boot sequence loads both the kernel and user program images at system startup time. The resulting system allows the default memory manager to be built and run in a standard user-level environment, but still operates with the high reliability required by the Mach kernel.

The default memory manager is bundled with another component of the Mach 3 system: the bootstrap service. This service starts the initial set of system servers that make up a complete operating system based on the Mach 3.0 kernel. Since the real file system may be one of these servers, the bootstrap service needs its own copy of a subset of the file system. This is shared with the default memory manager. Placing these two components outside the kernel allows them to be easily reconfigured with different file systems.