> 7 Backpressure > Was that the intention of the artist? You decide—is the wheel in the pipes a clever reference to UNIX back pressure, or is that a stretch?

Maybe? That wheel is a valve handle BTW. A closed valve in a fluid system would cause back-pressure upstream as no flow will allow the pressure to build to what ever maximum the source can provide. Valves which control flow (globe valve) can also act as a crude pressure controller if partly open allowing only a small amount of flow causing back pressure to build. In the case of Unix pipes, back pressure occurs when the writer fills the pipe's buffer before the reader consumes it causing the writer to hang. Now both procs are doing nothing bringing your data assembly line to a grinding halt. Not good for production.