Asynchronous I/O in NetBSD
A few days ago, Mindaugas Rasiukevicius committed
to NetBSD, a way to initiate input/output operations and
have the system return before they have ended (== running them asynchronous).
When I/O is actually done, the initiating process is usually notified
via a signal. See
Single Unix Specification.
Mindaugas also has
a page with details of NetBSD's implementation of Asynchronous I/O.