The Surprising Story Behind How ‘The Oregon Trail’ Was Built Without Access To A computer

When The Oregon Trail came out in 1971, it was unlike any game that had come before. An educational computer game that kids actually wanted to play, it filled with action-packed hunting scenes, RPG-like strategy and story, and the constant threat of death. It also made “dying of dysentery” an in-joke for children of the 70s, 80s, and 90s (such was the game’s lifespan).

But the most amazing thing about The Oregon Trail is perhaps how it was made. Coded by three college students in the days before personal computers, its creators built the game over the limited hours they could teletype into a central mainframe. And with little before it spell out how these games should look or play, its creators had to come up with novel solutions to just about every problem they encountered. 

Here’s how they did it, as told by co-creator Don Rawitsch.

Screenshot: The Oregon Trail

A moment from the original Oregon Trail that has sparked modern memes

On Programming A Game Without Steady Access To A Computer

The Oregon Trail computer game was co-invented in 1971 by myself, Bill Heinemann, and Paul Dillenberger; three teachers in training from Carleton College, Northfield, Minnesota. It was a time before the advent of personal computers, and the only way a school could provide computer access to its students was to connect a text-only teletype via phone line to a large mainframe computer housed in a special facility, often a local university. Given that this meant only a small percentage of schools had such access, computers were used mostly in the teaching of coding. There was no K-12 market yet for pre-made applications.

The mainframe computers usually had a library in which users could store and share programs they created. Thus, our team had experience with simple simulations, such as running your own lemonade stand, taking into account local tastes, cost of goods, pricing, and weather to maximize the stand’s profit. Other than these few examples, there were no antecedents to examine; no commercial games, no books written about creating computer games, and no collegiate classes taught on the subject.

Bill, Paul, and I did have an understanding of how an event could be simulated mathematically by setting up algebraic relationships between variables that represented the impact of user decisions, the financial value of supplies, and random events. When I found myself faced with teaching a unit on U.S. westward migration, the three of us decided to try making a computer game.

On Using History And Math To Create Realistic “Probabilities” For Random Events

The Oregon Trail would probably have been successful if the probabilities chosen for events along the Trail had been educated guesses: “It probably rained 25 percent of the time, so let’s have the computer report rain in one of every four turns.” Not content with this approach, I found books in the library that published the actual diaries of pioneers traveling the Trail. I kept a record of what happened each day of the trip for several of these diaries, and then set the probabilities based on this information. For example, if the diaries averaged reports of rain in 27 days of the 180-day trip, the computer probability for rain was set for 15 percent.

It would have been easy to decide that for the game: “the probability of snow will be seven percent.” However, the pioneers typically made the six-month journey during the April to September period. During these warm months, it almost never snowed on the prairie traversed during the trip’s first half. Once the Trail entered the Rocky Mountains, snow was more likely. This was followed by more flat land with little snow, and then came the Cascade Mountains in fall with a higher likelihood of snow.

The snow probability in the game was defaulted to zero during miles 0 to 950 of the trip. Bill and Paul developed a parabolic formula that, when graphed, produced an upright U-shaped curve covering miles 950 to 2000, with mileage along the X-axis. During each turn through that segment of the trip, the computer generated a random number that was compared to the curve. If the random number fell under the curve, as it often did at the curve’s beginning and end, snow occurred, representing the two mountain ranges. If the number fell above the curve, as it often did during the mileage between the ranges, snow was less likely. Using different curve formulas, this technique was used for several of the game’s variables to produce different event probabilities as a function of trail location.

On Building The Game’s Iconic “Hunting” Mechanic

So many computer games today involve shooting. You come to take it for granted. However, with this historical era, shooting was a part of the story. The pioneers depended on their guns for hunting and protection. But the teletype in 1971 did not have color, graphics, animation, or sound effects. It could only print text on a scroll of paper. How, then, to include rifle use in the game?

Bill ingeniously solved this problem. He took advantage of two of the teletype’s capabilities: It recognized whether the user’s typed input matched what was specified in a program, and it could measure the elapsed time between the end of a computer instruction sent to the user and the typed input of the user’s response. When use of the rifle was called for in Oregon Trail, say for hunting, the computer sent the instruction, “Type BANG,” or some other randomly selected gunshot word. The user would comply on the keyboard as quickly as possible. If he typed the word incorrectly, he earned no food for his efforts. If the word was typed correctly but slowly, he earned some food. A correctly typed word entered quickly resulted in a lot of food being added to the user’s supply. Middle school students who had never considered learning typing skills soon had a very motivating reason to do so!

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