The simulator or "sim" is the term used by Linden Lab for the software that supports a Region, though the terms are commonly used interchangeably. Each simulator runs a 256m x 256m (65,536 sqm) area in Second Life in which all things for that area exist (land, avatars, objects, etc). DaBoom is an example of a sim. The world/grid of SL is made up of many sims linked together to make a continuous area. Up to four (4) sims can be hosted on a single server as each sim takes roughly the equivalent of a single CPU to run (the sim class is a measure of how many sims run on a particular server).