I was going to post and say shared memory and reach the end of my knowledge in about 1 line- then I did a quick search and found this:
http://developer.apple.com/documenta...section_4.html
so I'll pretend I understand all these terms..!
Anyway - this seems a pretty good document..
I have also used things like JMS - but this is not really the tool for most inter-process communication on a local machine - and certainly uses plenty of system resources.
Euain