Game engine

A game engine is a piece of software used to power and control a game. An engine is tasked with various different game-related mechanics such as graphics rendering, physics, sounds, scripting, animations, AI and resource management.

Usage in The Sims series
The Sims series utilizes a new, in-house, game engine for each base game, with expansion packs and stuff packs being built on the same engine for that specific game. For example, The Sims 2 introduced a 3D engine with visual and technical advances over its predecessor while its sequel, The Sims 3 brought in a newer version of the engine that incorporated further visual enhancements with a fully fledged texture streaming solution to accommodate the open world.

Spin-off titles utilize a modified version of the newest available engine. An example of this is how The Sims Stories uses a modified version of the engine from The Sims 2 by decreasing the system requirements in order to make the game "laptop friendly". The Sims Medieval utilizes a modified version of the game engine from The Sims 3 with rendering enhancements.

Console titles used different engines, until The Sims 3 for console due to hardware differences. The Sims for console used a 3D rendering engine unlike its PC counterpart but limited gameplay to one floor per lot and implemented the object limiter. The Sims: Bustin' Out used an engine which featured visual enhancements on the original console engine as well as rendered load screens. The Urbz: Sims in the City up to The Sims 2: Castaway utilized a 3D engine which was incrementally updated with each game, The Sims 2 for console adding a "direct control" system allowing for third-person control over Sims as opposed to the traditional "point and click" system. The Sims 3 for console uses a "watered-down" version of the PC version's engine with the object limiter applied and the texture streaming solution omitted due to the console's RAM limitations but allows for multiple floors to be constructed and used on a lot.

The Sims Engine
This is the first engine used by the series. It uses a variation of 2D and 3D graphics, with Sim models being of a high polygon count while objects are pre-rendered.

This engine is used by these games:
 * The Sims
 * The Sims: Livin' Large
 * The Sims: House Party
 * The Sims: Hot Date
 * The Sims: Vacation
 * The Sims: Unleashed
 * The Sims: Superstar
 * The Sims: Makin' Magic

The Sims 2 Engine
This is the second engine used by the series. It replaces the isometric view of the original game with a full 3D rendering system. The newer engine also allows for easy distribution of mods and custom content, thanks to the  file support.

This engine is used by these games:
 * The Sims 2
 * The Sims 2: University
 * The Sims 2: Nightlife
 * The Sims 2: Holiday Party Pack
 * The Sims 2: Open for Business
 * The Sims 2: Family Fun Stuff
 * The Sims 2: Glamour Life Stuff
 * The Sims 2: Pets
 * The Sims 2: Seasons
 * The Sims 2: Celebration! Stuff
 * The Sims 2: H&M Fashion Stuff
 * The Sims 2: Bon Voyage
 * The Sims 2: Teen Style Stuff
 * The Sims 2: FreeTime
 * The Sims 2: Kitchen & Bath Interior Design Stuff
 * The Sims 2: IKEA Home Stuff
 * The Sims 2: Apartment Life
 * The Sims 2: Mansion & Garden Stuff
 * The Sims Life Stories
 * The Sims Pet Stories
 * The Sims Castaway Stories

The Sims 3 Engine
This is the third engine used by the series. As well as numerous visual improvements such as texture quality, shader quality and lighting, the engine features improved animations and a texture streaming solution to allow for an open neighborhood without frequent loading screens.

This engine is used by these games:
 * The Sims 3
 * The Sims 3: World Adventures
 * The Sims 3: High-End Loft Stuff
 * The Sims 3: Ambitions
 * The Sims 3: Fast Lane Stuff
 * The Sims 3: Late Night
 * The Sims 3: Outdoor Living Stuff
 * The Sims 3: Generations
 * The Sims 3: Town Life Stuff
 * The Sims 3: Pets
 * The Sims 3: Master Suite Stuff
 * The Sims 3: Showtime
 * The Sims 3: Katy Perry's Sweet Treats
 * The Sims 3: Diesel Stuff
 * The Sims 3: Supernatural
 * The Sims 3: Seasons
 * The Sims 3: 70s, 80s, & 90s Stuff
 * The Sims 3: University Life
 * The Sims 3: Island Paradise
 * The Sims 3: Movie Stuff
 * The Sims 3: Into the Future
 * The Sims Medieval
 * The Sims Medieval: Pirates and Nobles
 * The Sims 3 for console
 * The Sims 3: Pets for console

SmartSim (Updated November 2017)

 * The Sims 4
 * The Sims 4: Outdoor Retreat
 * The Sims 4: Get To Work
 * The Sims 4: Luxury Party Stuff
 * The Sims 4: Perfect Patio Stuff
 * The Sims 4: Spa Day
 * The Sims 4: Cool Kitchen Stuff
 * The Sims 4: Spooky Stuff
 * The Sims 4: Get Together
 * The Sims 4: Movie Hangout Stuff
 * The Sims 4: Romantic Garden Stuff
 * The Sims 4: Dine Out
 * The Sims 4: Kids Room Stuff
 * The Sims 4: Backyard Stuff 
 * The Sims 4: City Living
 * The Sims 4: Vintage Glamour Stuff
 * The Sims 4: Vampires
 * The Sims 4: Bowling Night Stuff
 * The Sims 4: Fitness Stuff
 * The Sims 4: Toddler Stuff
 * The Sims 4: Parenthood
 * The Sims 4: Cats And Dogs 
 * The Sims 4: Laundry Day Stuff (TBA: 2018)