Hey, now this is cool... DM instructor Mark Smith blogs about his quest to solve once and for all the mystery of how concurrent GC works in .NET.

I remember discussing this a few months back with Andy Clymer and Rich Blewett, DM instructors themselves.  We couldn't come to a conclusion in the little time we spent on it... glad to see the case has been cracked!

To summarize... concurrent GC (which trades off responsiveness in GUI apps for increased resource consumption and longer total time spent doing GC) can occur on single- and multi-threaded machines, and is the default in the workstation version of the GC (concurrent GC makes no sense in the context of a server app).