What are different types of UNIX?

One of the strengths of Unix has always been interprocess communication. Amongst the facilities provided by the OS are so called pipes. These pipes connect the output of one Unix process to the input of another. This is fine if both processes are living in the same parent process space, started by the same user. There are however circumstances where the communicating processes must used named pipes. One such circumstance is that the processes have to be executed under different user names and permissions.