BugOS is a microkernel operating system. It has a kernel, device drivers, a file system, and an Internet module. The main concepts are that every process has its own computer with its own console, security, and modularization. If a process wants to read the file, it asks the kernel. The kernel forwards the request to the filesystem driver, which reads and writes through the partition handler, which operates over the idehdd driver. The kernel is around 20 KB. Processes are fully separated from hardware.
GNU Mach is the microkernel upon which a GNU Hurd system is based. It provides an Inter Process Communication (IPC) mechanism which the Hurd uses to define interfaces for implementing in a distributed multi-server fashion the services a traditional operating system kernel provides. Mach is particularly well-suited for SMP and network cluster techniques. Thread support is provided at the kernel level, and the kernel itself takes advantage of that. Network transparency at the IPC level makes resources of the system available across machine boundaries.