This mechanism makes it possible to increase the number of participants while still displaying the collective image in a fixed-size area of the screen. So, the personal sign of the first participant will initially take up the whole global image. Then, the part devoted to this sign will decrease in size as other users connect themselves to the current session. Moreover, the PG program automatically determines the location of new personal images inside the global one. These personal images are either set side by side in a spiral-like shape or are set in such a way that they will replace the image of a user who just left the session.
Participants can also communicate by exchanging textual messages through email.
Other users can either be identified by their login name or by clicking in the part of the collective image that corresponds to their personal sign. Finally, PG also provides a history mechanism. Each participant must first download the appropriate version of the PG program for his own computer through the Web. The user interface is currently based on the X Window system and the Motif toolkit but will evolve to a Java version in the future in order to allow portability capabilities to other operating systems. The network interface is based on Internet Multicast.