The service nodes are where the processing work is done. When you assign a group of
service nodes to a cluster, they function as one very powerful computer because all their
resources are shared. If one service node is overloaded or otherwise inaccessible, another
service node is used.
You make a computer available as a service node by configuring it in the Apple Qmaster
Sharing window, accessible from Compressor by choosing Share This Computer from the
Apple Qmaster menu.