[[Liedtke]] explains in [On Microkernel Construction](http://l4ka.org/publications/paper.php?docid=642)
that a microkernel attempts to minimize the mandatory part of the operating
system by providing the minimal number of [[mechanism]]s that
maximize the flexibility of implementation (by imposing minimal
[[policy]]) while allowing the efficient implementation of the
remainder of the system.

The idea of a microkernel as explained above was first explored
by Per Brinch-Hansen in 1970 in
[The Nucleus of a Multiprogramming System](http://brinch-hansen.net/papers/1970a.pdf).

Other notable microkernels include Hydra, KeyKOS, Eros and L4.

An [introduction](http://www.cs.cornell.edu/Info/People/ulfar/ukernel/ukernel.html) by 
Úlfar Erlingsson and Athanasios Kyparlis (from 1996) to microkernel concepts.