Editing Microkernel (section)

== Nanokernel ==
The term ''nanokernel'' or ''picokernel'' historically referred to:
* A kernel where the total amount of kernel code, i.e. code executing in the privileged mode of the hardware, is very small. The term ''picokernel'' was sometimes used to further emphasize small size. The term ''nanokernel'' was coined by Jonathan S. Shapiro in the paper [https://web.archive.org/web/20110621235229/http://www.cis.upenn.edu/~KeyKOS/NanoKernel/NanoKernel.html ''The KeyKOS NanoKernel Architecture'']. It was a sardonic response to [[Mach (kernel)|Mach]], which claimed to be a microkernel while Shapiro considered it monolithic, essentially unstructured, and slower than the systems it sought to replace. Subsequent reuse of and response to the term, including the picokernel coinage, suggest that the point was largely missed. Both ''nanokernel'' and ''picokernel'' have subsequently come to have the same meaning expressed by the term microkernel.
* A virtualization layer underneath an operating system, which is more correctly referred to as a [[hypervisor]].
* A [[hardware abstraction layer]] that forms the lowest-level part of a kernel, sometimes used to provide [[Real-time computing|real-time]] functionality to normal operating systems, like [[Adaptive Domain Environment for Operating Systems|Adeos]].

There is also at least one case where the term nanokernel is used to refer not to a small kernel, but one that supports a [[nanosecond]] clock resolution.<ref name="udel">{{cite web|url=http://www.eecis.udel.edu/~mills/database/papers/nano/nano2.pdf|date=28 November 2000|title=The Nanokernel|author=David L. Mills and Poul-Henning Kamp |access-date=28 August 2017}}</ref>