Cities: Skylines is an open-ended, city building simulation game that lets players create the city of their dreams—or nightmares. It's flexible enough to be used to create computers, too, as it turns out. Software engineer Dániel Bali used Cities: Skylines to create a 4-bit computer that's able to do simple addition.
"The adder does pretty much what humans do when they add numbers on paper, except instead of base-10, they use base-2," Bali said. (The base-2 number system is the binary system, which uses only 1 and 0.)
Using power plants, water towers, and sewage pipes, Bali created the "AND" and "OR" gates needed to complete the calculations. A flooded power plant or wind turbine is the "NOT" gate. The 1s and 0s are represented in the power lines in Cities: Skylines, Bali told VICE. If they're powered up, they're a 1. If they're not, they're a 0. The logic gates are connected by the power lines, one going in and another going out.
"For example, an AND gate will output 1 if both of the inputs are 1," Bali said. "An OR gate will output 1 if either of the inputs are 1. Finally, a NOT gate will output the opposite of what is on its input."
Bali set up the computer using unlimited money in-game and a custom map that's set up like a grid. "It starts with the rightmost digits and adds them," he said. "If the result is too big to fit in one digit, it carries forward a 1 to the next place, and so on. This happens to 4 bits and because there is a final carry value, the result can be up to 5 bits long."
But the unpleasant—some would say nightmare—scenario for the residents of Bali's Cities: Skylines creation is that the system is powered by poop. Just outside the computer system, he set up a city that can produce enough waste to flood a wind turbine. "Because if the turbine is flooded, it won't produce any power," Bali said. "I needed to have a city that produces enough virtual waste water to operate these sewage pipes." These are essential for the NOT gates, of which there are eight in the system. Without them, the computer just wouldn't work.
But a poop-powered system isn't a "green" solution for the Cities: Skylines creation, Bali added. "Each gate uses an oil power plant, so the pollution is quite bad," he said in his blog.
The computer created in Cities: Skylines is very slow; Bali said it takes 15 in-game months to compute the simple addition problem. (That's 20 minutes in real-life). Bali told VICE the computer took two-weeks to build, too.
When asked why he wanted to create a poop-powered calculator in Cities: Skylines, he said he didn't know. "I like to do weird things with computers," Bali said. "Just to see if it would really work, I guess."