FILE: sockets/non-socket

pipes -- designed for 1-way (half duplex) communication.  Can be used
	for 2-way (full duplex), but it's very complicated.  Only on
	same host.

files -- can be across hosts if there is NFS.

shared memory -- only on same host.

signals -- only on same host.  limited amt of information.

RPC -- between hosts.  Includes mechanism (XDR) for
	architecture-independent data (sockets must use the byte-order
	conversion macros described in byteorder(3n).  Don't know much
	about it from programming perspective.