Microkernel

A renewed interest in this design structure came with the proliferation of the Xen VMM software, ongoing discussion on monolithic vs. micro-kernels (particularly in Usenet newsgroups and Web forums), Microsoft's Ring-1 design structure as part of their NGSCB initiative, and hypervisors based on x86 virtualization such as Intel VT-x (formerly Vanderpool).

The monolithic model differs from other operating system architectures (such as the microkernel architecture) in that it alone defines a high-level virtual interface over computer hardware.

Mach is often mentioned as one of the earliest examples of a microkernel.

QNX was one of the first commercially successful microkernel operating systems.

For example, modern microkernels generally only provide a synchronous messaging primitive and asynchronous messaging can be implemented on top by using helper threads.

IPC is very important to the design process for microkernels and nanokernels, which reduce the number of functionalities provided by the kernel.

GNU Hurd is a collection of microkernel servers written as part of GNU, for the GNU Mach microkernel.

This was designed as a modified microkernel, as the Windows NT kernel was influenced by the Mach microkernel developed by Richard Rashid at Carnegie Mellon University, but does not meet all of the criteria of a pure microkernel.

L4 is a family of second-generation microkernels, used to implement a variety of types of operating systems (OS), though mostly for Unix-like, Portable Operating System Interface (POSIX) compliant types.

Debian GNU/Hurd is a flavor based on the Hurd microkernel, instead of Linux.