A pipe in the SunOS 5.6 system is a mechanism that provides a communication path between multiple processes. Prior to SunOS 5.0, SunOS had standard pipes and named pipes (also called FIFOs, or first-in first-out). With standard pipes, one end was opened for reading and the other end for writing, thus data flow was unidirectional. FIFOs had only one end and typically one process opened the file for reading and another process opened the file for writing. Data written into the FIFO by the writer could then be read by the reader.
To provide greater support and development flexibility for networked applications, pipes and FIFOs have become STREAMS-based in SunOS 5.x. The interface is unchanged but the underlying implementation has changed. When a pipe is created through the pipe(2) interface, two Streams are opened and connected. Data flow is serial.
The remainder of this chapter uses the terms pipe and STREAMS-based pipe interchangeably for a STREAMS-based pipe.