The plasma panel displays lessons and the student input, but the CDC Cyber-70 handles every electric signal, both those produced in Champaign-Urbana and those produced by the students and authors scattered through-out the country. This is made possible by the unique time-sharing aspect of PLATO. Each lesson written by a PLATO author is stored on large disks, read electronically by the computer, and sent out to the terminal — in an Urbana grade school, in the building itself, or in

Tucson, Princeton, Sweden, Canada, Florida, or wherever a terminal is located.

The student sees a question displayed on his screen and types in an answer. The answer does not go from the keyboard directly to the screen; it returns to Urbana, is processed into computer language, and is returned over the same telephone wires that carried the question to be displayed on the screen within microseconds of the student's pressing the keys.

If this were done on a one-to-one basis, very few students could use the system at any given time. However, the student is continually being "swapped" out of the central memory of the computer into an "area" known as "Extended Core Storage" (ECS). From ECS the student is swapped in and out of the central computer core memory thousands of times each minute, taking him out and bringing him back so rapidly that he may not even be aware of the pause. In this manner, the 900 terminals can theoretically be in use all at once; 300 or 400 are the most that seem to be in use at any given minute because of the difference in time zones and class schedules across the country. When the student signs off, the lesson he is working on is returned to the disk for storage until some other student calls it forth again. The computer keeps track of each student's work and has a capacity of not only grading it, but of being able to remember where the student left off and returning there when instructed to do so.

Lessons are written by PLATO authors in a computer language called TUTOR, which is largely the creation of Paul Tenczar, an icthyologist turned computer man. Tenczar found the standard computer languages for writing lessons to be difficult and restrictive. Tenczar's TUTOR is a language which noncomputer people can begin to learn

very quickly but which computer people sometimes find very "uncomputerlike." That Tenczar is an icthyologist and Bitzer an electrical engineer is not unusual in CERL, which has few or perhaps none of the typical "computer types" — a fact which CERL people regard as contributing to the success of the system.

Many other people besides Bitzer and Tenczar have contributed to PLATO. The brilliant minds attracted to PLATO have introduced "external devices" that can play music, show slides on the plasma panel, simulate the controls of an airplane or automobile, and do many other things. To mention just some of these contributors — William Golden, Dominic Skarpedos, Bruce Sherwood and Richard Pribst — one drops names familiar to every PLATO author but also omits many others who have contributed to PLATO. There are dozens of PLATO authors, writing lessons in hundreds of fields. Almost every academic discipline is represented in PLATO'S offerings. History is the most notable holdout, but history courses may soon be under development. The TUTOR language makes it possible for scholars with little or no background in computers to begin to develop lessons and courses.

Amazing as PLATO is now, its potential is even greater. Authors can write each other memos through the computer, and even "call" each other as if they were using a writing version of the telephone. People thousands of miles away can monitor each other's terminals and benefit from firsthand appraisal of each other's lesson writing. Work is being done now on developing PLATO terminals that could perhaps be plugged into home cable TV sets, giving people in their homes the chance to learn about Chaucer or French verbs, or chemistry, physics, aeronautics.

The extension of a university into the community is often talked of but rarely done except through "adult education" classes requiring the physical presence of teachers and students or radio courses which cannot answer you back. Some day a university class may go on in your living room —whenever you want to turn to the keyboard. Reference works may be immediately available, and instant written communications will some day be possible. New forms of recreation and communication will undoubtedly develop. As capability of the system grows, one can even imagine the world in the future being tied together to a PLATO network, joining Marshall McLuhan's dream of a "global village" with a bent towards the written word and a literate format which some people find frighteningly lacking in TV. This may seem like far-fetched dreaming, but so did the PLATO network less than 15 years ago.

There will be a cost advantage as well. Though a terminal is now rather expensive, mass production will bring the cost down, possibly within the range of a medium-priced color TV set. Even at current cost, the wealth of instructional materials available could not be purchased at any price. PLATO terminals will never replace the teacher; not only will teachers be needed to produce and to supervise the electronic lessons, but even PLATO, with all its accomplishments cannot handle a free flow of dialogue or essay examinations without human intervention. But the vision held in common by so many of the people at CERL of massive amounts of educational materials ready to assist the teacher — or waiting just the other side of an electric switch in the home — makes Illinois' contribution to the future of public education and interaction between learned men and learners a magnificent one, possibly unmatched by any development in educational technology since the invention of printing.