Answer: RollerCoaster Tycoon

The 1999 smash-hit simulation game RollerCoaster Tycoon was not only well received by gaming critics, but purchased in droves by simulation fans who couldn’t get enough of the quirky amusement park simulation game.

For the era in which it was created, the game had surprisingly complex simulation algorithms and snappy game play. What many fans may not realize is that the excellent performance of the game was due almost entirely to the game creator, Scottish game developer Chris Sawyer, writing 99 percent of the game in assembly code. Assembly code, for the unfamiliar, is what is known as a low-level programming language that requires a lot more effort to work with than higher-level programming languages because the language has a closer one-to-one association with the actual functions of the computer hardware. The only part of the game that wasn’t written in assembly code was a small bit of code that interfaced the game software with the operating system.

Today it would be unheard of to program a complex video game in assembly language but, at the time, it was the only way for Sawyer to get the performance out of 1990s-era hardware he needed to make the game as enjoyable and complex as he wanted.