the book · contents

03-old-parts 3,461 words about 15 min

Chapter 3. Old parts

Your steward reports once a year. The city has so many people, the harvest yielded so many bushels an acre, the rats ate so many, and land is trading at a price somewhere between 17 and 26 bushels an acre. Then he waits for three numbers. How many acres to buy or sell. How many bushels to feed the people. How many acres to plant. Grain is food, seed, and money at the same time, so every bushel you hand out to keep people alive is a bushel you cannot plant or spend on land. You type your answers and the year resolves. A plague may halve the population. If 45 percent of the people starve in a single year, you are thrown out of office and the game ends.

That is Hamurabi, written in 1968 for a PDP-8. It has ten turns, three stocks, three decisions, and a few random draws, and the catalog lists 6 mechanics in it. Every one of them is still in use: crops that return a random yield, random disasters, goods that a population consumes, a turn structure, spoilage, and an advisor who reports the state of the kingdom. Crop cultivation alone appears in 25 catalog games, among them Stardew Valley, where it is a core mechanic.

Most of the parts were in place by 2000, and a test against chance shows how much of that comes from early invention and how much from the parts being widely shared.

Dating a mechanic

The dataset dates each mechanic by the release year of the earliest catalog game that uses it. That date is a lower bound. A mechanic can be older than its first catalog game for two reasons: an earlier game that used it is missing from the catalog, or the idea came from somewhere that was never a computer game at all. Both happen often, and the records say so.

Hamurabi itself was written from a description of an older program, The Sumerian Game of 1964, which the catalog does not hold. SimCity grew out of the map editor Will Wright built for a helicopter game and took its model of urban growth from Jay Forrester's book Urban Dynamics. Railroad Tycoon came from a board game, 1830, and cited SimCity. Civilization put together the technology tree of Francis Tresham's board game, the conquest of an earlier computer game called Empire, and Railroad Tycoon's habit of running several systems at once. The Sims borrowed its idea of a house from Christopher Alexander's A Pattern Language. Factorio grew out of two Minecraft mods, IndustrialCraft and BuildCraft, that added pipes and machines. Simulation games borrow from board games, academic models, architecture, and each other's mods, and a catalog of games sees only the point where an idea entered a game it holds.

The edges of the catalog produce a few odd firsts. The earliest catalog game with a pause button and with free placement is Conway's Game of Life, from 1970, because seeding cells on a grid and choosing how fast the generations run are those two mechanics in their barest form. Europa Universalis IV, from 2013, is credited with dynasty succession, interest groups, war score, and religious conversion, but the catalog holds no earlier Europa Universalis game. And Utopia, often called the first city-building game, carries the status "contested" because sources disagree on whether it came out in 1981 or 1982.

"First appears in" means "first appears in a game this catalog holds". The catalog is also thin before 1990: it holds 3 games from the 1970s and 7 from the 1980s, against 75 from the 2010s.

Most of it by 2000

Even so, the count is lopsided. Of the 199 mechanics in the vocabulary, 137 appear in at least one catalog game released in or before 2000, which is 69 percent. Those games number 37, 21 percent of the catalog. By decade of first appearance, the 1990s lead with 80 mechanics and the 1980s follow with 39; together the two decades account for 60 percent of the vocabulary. Then the count falls: 32 in the 2000s, 29 in the 2010s, and 4 so far in the 2020s, a decade not yet over.

The vocabulary, year by year

Figure: The vocabulary, year by year. Cumulative mechanics by the year of their first catalog game, one layer per family, oldest families at the bottom. Labels mark the years that added the most mechanics and the game that introduced most of them. Drag the year control, or hover or tap the chart, to read what each year added. Interactive version: https://sim.yohei.me/#fig-strata

The figure stacks the vocabulary year by year, one layer per family. The steepest single years are 1989, when SimCity and Populous came out, and 2013, the year of Europa Universalis IV, Factorio, Papers, Please, and BeamNG.drive.

A test of the claim

A count like that suggests a golden age of invention followed by decades of reuse, and the suggestion can be tested against chance.

Any catalog game uses about a dozen mechanics, and most mechanics are shared by several games, so any small set of games will show a good part of the vocabulary. The question is whether the games released by 2000 show more of it than another set of the same size would. The build answers it by drawing random sets of 37 catalog games from every era, trimming each drawn game to the size of one of the early games, and counting how many mechanics each set covers. Over two thousand draws, a random set covers 129 mechanics on average, 65 percent of the vocabulary, against 137 for the real early games. Random sets match or beat the early games in a share of 0.11 of draws.

So the early games cover a little more of the vocabulary than chance would give them, and the difference is too small to rely on. Most of the "set early" figure reflects how widely the parts are shared: a few dozen games of any period already show most of the vocabulary. Two narrower findings survive the test: invention concentrates in a small number of games in every decade, and later games are built mostly from parts that already existed.

The founding games

A small number of games introduced a large share of the vocabulary. SimCity is credited with 10 mechanics: zoning, land value, the three demand valves for homes, shops, and industry, the power grid, service coverage, crime, pollution, traffic, fire spread, and taxation. Its model is the set of coarse maps described in chapter 2, and the 2008 source release, under the name Micropolis, made their rules readable.

Civilization and Railroad Tycoon are credited with 7 each. Civilization's include the tech tree, fog of war, and policy choices; Railroad Tycoon's include loans, scheduled vehicle routes, rail signals, and a timeline that makes new locomotives available on historical dates.

M.U.L.E., from 1983, introduced 6, among them the production chain and prices set by supply and demand. Its four resources depend on each other: food sets how long a player's turn lasts, energy shortages stop plots from producing, and the supply of smithore sets what the robots cost. Prices come out of live auctions in which players walk their avatars toward a price. Danielle Bunten also built catch-up rules into the systems: tied bids go to the player who is behind, and harmful random events never hit the player in last place. The taxonomy has no mechanic for catch-up rules yet; the record files it as a proposal.

Little Computer People, from 1985, introduced 6: needs that decay, personality traits, daily schedules, care of a creature, procedurally generated characters, and natural-language interaction. The resident of the house reads typed requests and decides whether to comply depending on his mood. Every copy of the disk seeded a different resident from its serial number, with one of 256 names, its own shirt color, and its own personality.

Elite (1984) introduced generated terrain, trade routes, reputation, and milestones; its eight galaxies of 256 systems were regenerated from a seed rather than stored, which let a universe fit in an 8-bit machine. The Incredible Machine (1993) introduced modular assembly, rigid-body physics, signal circuits, and sharing designs with other players; its physics has no random number generator, so a machine behaves the same on every run and a solution can be checked. Theme Park (1994) gave every visitor a record of about 200 bytes and introduced choosing an action by scoring options against needs, the architecture that The Sims made famous six years later. Creatures (1996) introduced learning creatures, contagion, and an inspector for a creature's insides; chapter 6 returns to its Norns. The Sims added 3 of its own: smart objects that advertise what they offer, social exchanges, and levels of autonomy.

Smaller founders fill in the rest of the early record. Lemonade Stand (1973) reduced a business to three daily choices, how many glasses to make, how many advertising signs to buy, and what to charge, set against the day's weather. Customers buy more at lower prices and with more signs, sales stop at the glasses made, and a thunderstorm on a cloudy day wipes out the day's investment [1]. It is the catalog's earliest game with customers choosing on value and with advertising. Utopia (1982) introduced 5, among them citizen satisfaction and unrest. Two players on one screen spend gold on buildings and boats over up to 50 rounds of 30 to 120 seconds, score points for how well their people are housed, fed, and kept content, and can pay to fund rebels on the other player's island [2].

Populous (1989) introduced god powers and terraforming, described in chapter 2. Princess Maker 2 (1993) is the catalog's earliest game with triggered event chains: events fire on the daughter's age, her attributes, and the season, and lead toward the endings chapter 4 describes.

Caesar III (1998) introduced 5, among them services delivered on foot. Each service building sends out a walker who roams the roads. A house the walker passes gets its coverage set to 96, which falls by 1 on each update until the next visit, so the same buildings serve a block well or badly depending on how its junctions turn the walkers [3]. Its developers cited SimCity's static placement as what they wanted to make less static [4].

Ultima Online (1997) introduced 5 mechanics of online worlds: a persistent world, crafting as the basis of a player economy, player organizations, loot taken from the dead, and zones that set where players may attack each other. Its record notes that a planned ecology, in which animals responded to ecological events, was removed during beta because players killed creatures faster than they could spawn, and that unrestricted killing between players led in 2000 to a split into one world where such combat was consensual and another where it was open [5].

What came after

The 2000s added 32 mechanics, several of them from online worlds where the other players are part of the simulation. A Tale in the Desert (2003) introduced elections, laws that players write and vote on, and a world that is wiped at the end of each Telling, about eighteen months; EVE Online (2003) a market almost entirely made by players; Second Life (2003) programs that players write into the world. Sequels added parts to their own series: public transit lines in SimCity 4, aspirations in The Sims 2, and requests from neighbours in The Sims 3.

Single-player games of the decade added a scattered set. Football Manager (2004) is the catalog's earliest game with dilemma cards: press conferences pose questions whose answers change morale and media relations. Silent Hunter 3 (2005) is the earliest with projectile ballistics, in its torpedoes, which run at a set speed, depth, and gyro angle toward an intercept the player computes from the target's speed and angle on the bow, so a bad solution misses. Nintendogs (2005) let nearby DS owners meet each other's dogs and exchange presents. The Powder Toy brought falling-sand materials, Universe Sandbox gravity between every pair of bodies, and DCS World damage to individual aircraft systems, all in 2008. The Sims 3 (2009) kept the households the player is not controlling aging, working, forming relationships, and moving around the neighborhood, a setting players can switch off.

The largest single source of new mechanics in the catalog came six years after the 2000 line. Dwarf Fortress (2006) is credited with 11, more than any other game: fluid and gas simulation, heat transfer, mood breaks, a hidden stress value, bodies made of layered tissues, rooms recognized from their walls, designated jobs, hauling, migrants drawn by a fortress's success, threat that grows with wealth, and a generated history of the world before the player arrives. Tarn Adams's stated method is to break each system into parts and base each one on a real-world analog.

From 2010 on, 33 mechanics appear for the first time. They come mainly from four lineages.

Factory games. Factorio introduced conveyor belts, machines boosted by modules, and logistics robots that carry items between requesting and providing chests. Conveyors spread fast for a recent mechanic: 9 catalog games use them, from Satisfactory to Big Pharma.
Grand strategy. Europa Universalis IV accounts for 7: interest groups, a currency of political capital spent on technology and stability, war score, conversion, dynasties, opinion modifiers, and tooltips that break each number into its causes.
Job simulators. Papers, Please introduced checking documents against rules that change day by day (2013), PC Building Simulator diagnosis and repair (2018), and House Flipper the tools that clean, paint, and tile a surface (2018).
Destructible materials. BeamNG.drive introduced vehicles built of nodes and beams that flex and break (2013), Space Engineers voxel destruction (2013), and SnowRunner terrain that deforms under wheels (2020).

A fifth source is new enough that it barely registers in the counts. AI Dungeon (2019) introduced generative content on demand, with no world state outside the text; chapter 7 opens with it. The research sandbox Generative Agents (2023) introduced gossip that spreads between characters. Chapters 7 and 8 follow these techniques. Gossip is one of the 4 mechanics first seen in the 2020s so far. The others, all from 2020, are Democracy 4's network of policies and voter groups, Townscaper's assisted building, and SnowRunner's deforming terrain.

Careers

A mechanic's first catalog game says little about when it caught on. Survival meters, stocks of food, clothing, and medicine that run down each round, are core in The Oregon Trail from 1971. The next catalog game with them is Minecraft, in 2009, and they reached a fifth game by 2013. Crops waited from Hamurabi to Harvest Moon, in 1996. Spoilage, the rats in Hamurabi's granary, reached its second catalog game in 2011: Project Zomboid, where food rots and refrigeration ends when the power fails, with Don't Starve a year later. Work priorities, the grid of colonists by jobs at the center of RimWorld, first appear as a supporting part of SimAnt in 1991, where the player sets the balance of an ant colony's workers, soldiers, and breeders and the workers divide their time between foraging, digging, and tending the brood; the next catalog game with them is Kenshi, in 2013. Long gaps like these are partly an effect of the thin early catalog, and partly real: the parts sat in a few games until a later design gave them a central job.

Other mechanics spread at once. Scenario objectives appear in Populous and SimCity in the same year, 1989, and reached a fifth catalog game by 1993. Conveyor belts reached their fifth catalog game in 2019, six years after Factorio. Factory games are a lineage that formed around one new part, and the clusters in chapter 4 treat them as a family of their own.

Built from older parts

The other finding that survives the test is how much recent games reuse. The catalog holds 118 games released in 2010 or later. Of all the mechanics they use, counting each game's uses, 84 percent are mechanics that already appeared in a catalog game by 2000. Of those games, 28 use nothing newer at all.

Factorio shows what reuse looks like in a game known for originality. Of its core mechanics, resource extraction dates in the catalog to Utopia (1982), production chains to M.U.L.E. (1983), the power grid and spreading pollution to SimCity (1989), the tech tree to Civilization (1991), and raid defense to Caesar III (1998); the attacks that grow with the factory date to Dwarf Fortress (2006). The one core mechanic that is new is the conveyor belt, and Factorio's identity rests heavily on it: each belt tier has a fixed throughput, and that cap shapes every layout a player draws.

Stardew Valley introduced nothing. Eric Barone built it in response to Harvest Moon (1996), which is the catalog's earliest game with seasons and with relationships to villagers. Its other core parts also appear in earlier catalog games: crops first in Hamurabi, an action budget first in Princess Maker 2 (1993) as three activity slots a month, and collection goals first in Gran Turismo (1997). Stardew sets its own numbers: friendship is a stock of 250 points per heart that loses 2 points on each day the player does not talk to the villager, and each day ends when the energy bar or the clock runs out.

Part of the reuse figure is arithmetic. Old mechanics have had decades to spread, and a mechanic introduced in 2020 has had a few years. The catalog also leans toward games that are famous and well documented in English, and its oldest entries are the canon of the form. With those limits, the data says that since 2000 most new simulation games have put known parts together in new proportions and tuned them, and a small number have added several parts at once.

Named influences

The records also name influences where a source states one, which gives a second, smaller view of the lineage. 50 games name at least one other catalog game, for 65 links in all. A game that names none may still have borrowed; its sources do not say so.

Three games are named most often, 5 times each: SimCity, The Sims, and Dwarf Fortress. SimCity is named by its sequel SimCity 2000, by Railroad Tycoon and Civilization, by Caesar III, and by Fallout Shelter. Civilization's record adds that an early prototype had a SimCity-style zoning layer, which was dropped [6]. The Sims is named by The Sims 2, by Paralives and inZOI, by Oxygen Not Included, and by the Generative Agents research town. Dwarf Fortress is named by Minecraft, Prison Architect, RimWorld, Oxygen Not Included, and Space Haven, whose developer describes it as RimWorld-style storytelling combined with a tile-based gas simulation [7]. Populous is named three times, by Black & White, by Civilization, and by From Dust, which was presented as its spiritual successor [8].

About a third of the links cross a subgenre line, 23 of 65. Civilization names a city builder, a god game, and a transport game: SimCity, Populous, and Railroad Tycoon. Oxygen Not Included names a colony sim, a management game, and a life sim: Dwarf Fortress, Prison Architect, and The Sims. Fallout Shelter names Little Computer People, SimCity, and FTL. Paralives, a life sim, names a city builder: its walls, which can curve, are drawn with a road-style tool inspired by Cities: Skylines.

Exercise: date a game

Pick a simulation game released in the last two years.

List its mechanics with the catalog's names.
For each one, look up its earliest catalog game and year on the mechanic's page.
Count how many are older than 2000, how many are from the 2000s and 2010s, and how many have no entry at all.
For each mechanic with no entry, write the four tests from chapter 1 against it: can it be named, is it atomic, does it have levers, could a game drop it. Those that pass are candidates for the taxonomy, and the dataset takes them as proposals.

If you have done this for Factorio or Stardew Valley, the result will look like the lists above: most of the parts are older than the game, and any new ones tend to carry its identity.

Factorio's parts come from a strategy game, a city builder, and a colony sim, yet when the dataset groups games by the parts they use, Factorio lands beside Satisfactory and shapez 2 in every subsample so far, and only sometimes beside the settlement builders it shares production chains with.

Sources

[1] Wikipedia contributors (2026). Lemonade Stand. Wikipedia https://en.wikipedia.org/wiki/Lemonade_Stand
[2] Wikipedia contributors (2026). Utopia (1981 video game). Wikipedia https://en.wikipedia.org/wiki/Utopia_(1981_video_game)
[3] bvschaik (2026). Julius: an open source re-implementation of Caesar III. GitHub https://github.com/bvschaik/julius
[4] Wikipedia contributors (2026). Caesar III. Wikipedia https://en.wikipedia.org/wiki/Caesar_III
[5] Wikipedia contributors (2026). Ultima Online. Wikipedia https://en.wikipedia.org/wiki/Ultima_Online
[6] Wikipedia contributors (2026). Civilization (video game). Wikipedia https://en.wikipedia.org/wiki/Civilization_(video_game)
[7] Bugbyte (2026). Space Haven. Bugbyte https://bugbyte.fi/spacehaven/
[8] Wikipedia contributors (2026). From Dust. Wikipedia https://en.wikipedia.org/wiki/From_Dust

Dataset dfde7895aa6d.