Before revision: The first is a ubiquitous minimal kernel, or microkernel, that directly controls that node's hardware.
After revision: <ref name="Nury J.|title=Centralized and Distributed Operating URL |url-access=registration|year=1992|publisher=Prentice Hall|isbn=978-0-13-122326-4</ref>The first is a ubiquitous minimal kernel, or microkernel, that directly controls that node's hardware.