|Behind the scenes|
An I/O Tower (or Input/Output Tower) is a location in the Computer World that programs use to communicate with their users. Programs regard these towers with reverence, and each tower has a Guardian to protect it. Notable Tower Guardians include Dumont and I-No.
Due to the vital service they provide, I/O towers are located centrally in their sectors. They can be identified by the powerful energy beams linking them with the outside world, which shine red when the channel is closed and blue when information flows through them. Programs who wish to communicate with Users, or sense that their Users are calling them, go to their local I/O Towers to communicate.
I/O towers were so essential that the MCP was reluctant to interfere with them, leaving Dumont's tower open in case his forces needed to "deal with the Other World once in a while," but eventually he appropriated a number of dissident Guardians and attempted to absorb their functions in hopes of making independently-operated Towers redundant. When the MCP was destroyed, the sky quickly lit up with blue I/O beams as freed programs resumed communication with their Users.
A program wishing to communicate through a Tower asks formal permission to enter it, and the Guardian, if allowing passage, responds with a prayer-like invocation. (Dumont's invocation was a direct quote from the I-Ching -- "All that is visible must grow beyond itself, and extend into the realm of the invisible.") The program then mounts the Guardian's dais and proceeds into the communication chamber beyond, where a platform rests below an opening to the communication beam. Standing on the platform, the program raises his or her Identity Disc and releases it to float upward into a flood of bright light, toward the beam that angles over the chamber. The disc passes through a dilating shield, converting into energy which shoots upward at high speed when it intersects with the beam. With the channel open, the program is able to converse directly with the User on the other end. When communication is complete, the disc returns the same way it came, bearing an imprint of the new information requested or delivered by the User (for example, Alan Bradley imprinted Tron's disc with the code needed to destroy the MCP).
- The red beam in which the MCP resided, which enclosed a dais incorporating a version of a Guardian's swiveling seat, was arguably an I/O beam as well.