The PLATO IV computer-based educational system contains its own communications hardware and software for operating plasma-panel graphics terminals. Key echoing is performed by the central processing unit: every key pressed at a terminal passes through the entire system before anything appears on the terminal's screen. Each terminal is guaranteed 1260 bits/sec of output at all time. There is no "store-and-forward" machinery, and output error and correction are integral parts of the system. (CH)