The gold standard of optimization: A look under the hood of RollerCoaster Tycoon

Summary

Due to some lucky circumstances, I recently had the chance to appear in one of the biggest German gaming podcasts, Stay Forever, to talk about the technology of RollerCoaster Tycoon (1999). It was a great interview, and I strongly recommend to listen to the whole episode here, at least if you speak german. If not, don’t worry—this article covers what was said (and a little more). RollerCoaster Tycoon and its sequel are often named as some of the best-optimized games out there, written almost completely in Assembly by their creator, Chris Sawyer. Somehow this game managed to simulate full theme parks with thousands of agents on the hardware of 1999 without breaking a sweat. An immensely impressive feat, considering that even nowadays a lot of similar building games struggle to hit a consistent framerate. So how did Chris Sawyer manage to achieve this? There are a lot of answers to this question, some of them small and focused, some broad and impactful. The one which is mentioned first in most articles is the fact that the game was written in the low-level language Assembly, which, especially at the time of the game’s development, allowed him to write more performant programs than if he had used other high-level languages like C or C++. Coding in Assembly had been the standard for game development for a long time but at this point in time was basically a given-up practice. Even the first Doom, which was released six years earlier, was already mostly written in C with only a few parts written in Assembly, and nobody would argue that Doom was in any way an unoptimized game. It’s hard to check for sure, but it’s likely that RCT was the last big game developed in this way. How big the performance impact was at the time is hard to quantify, but for what it’s worth, it was probably higher than it would be nowadays. Compilers have gotten much better at optimizing high-level code, and many optimizations that you’d need to do manually back then can be handled by compilers nowa...