In one of his more famous lines, poet William Butler Yeats asked, "How can you tell the dancer from the dance?"

If it didn't sound so pretentious, you might get away with asking the same question about programs and processes. A process is the image of a program as it executes rather than lies there on the disc, a process in potentia .

Really, this whole book is about processes; we're not talking about program design but about using the darn things.

Perhaps we're splitting hairs to break off this section. The chapters it contains could have fit in elsewhere. In the end, though, it seemed right to honor the somewhat tenuous link between the topics of managing processes ( Chapter 38, Starting, Stopping, and Killing Processes ), program and system performance ( Chapter 39, Time and Performance ), and offline execution ( Chapter 40, Delayed Execution ).