No compilations are necessary any more, once you created pvmsh and pvmwish. The shell program pvmsh can be seen as an enhanced version of the pvm console. The pvmwish interpreter has the same function as pvmsh, but in addition it has a lot of commands to build your own grapical user interface. There are buttons, entry widgets, menu's and so on. Now each process can have input and output through it's own X11-window.
Processes can spawn and kill each other and communicate through a pvm-channel.
It can be compared with the Tk 'send' command, only it works with sockets. In addition, pvmsh takes control of the event loop from Tcl, while pvmwish does the same with Tk. This is a very powerful command which makes programming an event-driven application much easier. To do the same in C or Fortran is much more difficult. PVM has no equivalent function for this.