A built-in Havok physics engine, detailed rendering, and dynamic lighting (with support for lighting effects like radiosity, distance fog, and glare) also contributed to the realism of Atmosphere worlds. Many world authors wanted to create large worlds, in order to build more realistic cities, for example, but such worlds would often take an excessive amount of time to load in the visitor's web browser, especially if the visitor was using a slower dial-up connection. To alleviate this issue, Atmosphere supported a pattern reminiscent of inline frames in HTML: sections of the world – "subworlds" or "models" – would load as the user neared, so that a city could load block by block, rather than all at once. One of Atmosphere's problems, however, was excessive memory usage, which was exacerbated by the use of advanced features such as embedded models and Flash movies in many worlds.