If viewers could look inside Star Trek's Holodeck, they would probably find advanced versions of the same kinds of equipment and software that virtual reality systems contain today. The heart of the system would surely be a powerful computer with programs that produce complex, three-dimensional images. Devices would send information from the computer to most or all of the crew members' senses: sight, hearing, touch, and probably smell and even taste. Other devices would pick up information about the members' body and hand movements, voices, and perhaps even thoughts, and would convey this information to the computer.

Drawing Virtual Pictures

The best virtual reality systems-the ones owned by large universities and corporations-use expensive supercomputers with special graphics capability, such as the Silicon Graphics Onyx series. Many home computers can create more limited...