Time limit

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Sprint uses a time limit.

A time limit is a game mechanic which requires the player to accomplish a goal within a determined length of time. Time limits have been used in gaming for hundreds of years to prevent players from taking too long in a game, but they have been used more recently as a way to add tension.

History

A chess clock from 1919.

Time limits have been an integral part of gaming for over a hundred years. The first professional chess match to use a time limit was in London in 1861 where hourglasses were used to keep time. By 1883, the inaccurate sand dials were replaced with fully mechanical gear-and-spring clockwork. Competitive sports also began incorporating time limits and the Football Association instituted a 90-minute soccer game in 1866 using mechanical clocks to keep time. As timekeeping devices became cheaper and easier to use, they became more integrated into gaming. For example, when the NBA formed in 1946, they used 12-minute long quarters, but eight years later in 1954, they introduced the 24-second shot clock. As fully automated games entered the entertainment market, electro-mechanical clocks were used to ensure a steady rotation of players, like in the 1955 electro-mechanical game K.O. Champ where the player's dime turned on the machine and kept it active for a set time limit. When fully-electronic video games came along, the time limit was already a staple game mechanic, so it was incorporated into early video games, including the very first commercial arcade title, 1971's Computer Space. Many of the arcade games in the 1970s were designed around time rather than attempts or lives, however, game designers quickly realized that players preferred to be rewarded for skilled play rather than have a set length of time, and the lives mechanic became the dominant mechanic. However, this introduced a new problem where especially skilled players would rarely die allowing them to effectively play forever. To prevent this, time limits were reintroduced in smaller sections of the game to force players to hurry. Over time, the sale of video games shifted from arcades to home consoles, and game designers no longer had to hurry players along. Rid of this confinement, even per-section time limits fell out of fashion. Today, time limits are still used in arcade games, racing games, sports games, or when the designer wants to increase a game's tension.

Usage

There are multiple ways time limits can be used in games. The two most common are per-game and per-section.

Per-Game

Night Driver uses a per-game time limit.

With a per-game time limit, players are given a set length of time for the entire span of the game, and, when the limit is reached, they get a game over. For example, when a player pays to play Night Driver, they buy a number of seconds. During that time limit, they yry to drive as far as possible. Crashing your car will slow you down, but you will keep being allowed to drive until the time limit is reached.

While this type of time limit was common in the 1970s, few video games still use it, although, games which simulate real life games with time limits, like sports or competitive chess, naturally still do.

Per-Section

You have only 2:20 to defuse the bombs in a section of Teenage Mutant Ninja Turtles.

A time limit per-section is a time limit that resets in each new section of the game. As lives became the dominant mechanic, arcade games saw the problem of especially skilled players being able to play effectively indefinitely, so game designers introduced time limits in each smaller segment of the game. This prevent players from taking too long by not only by forcing them to progress in the game, but also has the added effect of forcing them to play at a faster rate than they might otherwise play, thereby increasing the likelihood they will make a mistake. Donkey Kong 3 uses such a timer.

To add tension to a section of a game, a designer might introduce a time limit into a game that otherwise doesn't use them. For example, in area 2 of the Teenage Mutant Ninja Turtles home video game, several time bombs are set to detonate and the player must defuse them before the time limit.

Variations

Overtime

Overtime is additional time which is added to a game's time limit when players end a game with a tied score, usually used in sports as a way to prevent a tie. Games which end in a tie are not nearly as interesting to spectators as overtime, so most competitive sports which use scoring have instituted overtime in some form.

Warning

Many games implement a warning to let the players know when they're running out of time. This usually takes the form of a visual or auditory cue. An example of a visual cue occurs in the Atari 2600 game, Air-Sea Battle. Players are given a set length of time to shoot at targets, but the timer is not visible on the screen, so, to warn the players when time is running out, the scores at the top of the screen begin flashing about 15 seconds before time expires. An example of an auditory cue can be heard in Super Mario Bros. which not only has a warning sound, but also increases the tempo of the background music when you get close to running out of time.

Time Extension

Time extensions are bonuses the player can collect or earn which give them more time to play. These can be applied to per-game or per-section time limits.

Alternate Units

Although seconds are a standard unit of time, many games use timers with unique lengths of time. For many early video games, this was no doubt due to the difficulty of programming accurate seconds on the hardware of the time. However, alternate time units can also be used as a design decision. Having a clock tick faster can psychologically trick the player into feeling more rushed than they really are. Also, many early sports games often displayed long time limits, probably to make the players feel like they were playing a "real" game, but the clock often ticked twice as fast as it should, so the players didn't actually have to spend an entire afternoon on a single game. The 15 minute long periods in Nintendo's Ice Hockey actually only last for about 7 minutes.

Increased Difficulty

Taking too long in Berzerk causes Evil Otto to appear!

Some games tie their time limit not to the end of a game or the end of a character's life, but to increased game difficulty. For example, the game Berserk uses a hidden internal timer and, when it reaches zero, Evil Otto appears. Evil Otto is invincible, can move through walls, and doggedly chases the player. This is guaranteed death unless the player can quickly reach an exit to reset Otto's timer.

Time As Health

Time is health in Gauntlet.

The game Gauntlet was designed with a pretty novel take on the time limit by tying a character's health to a per-game time limit. When a player buys into the game, they are given a set amount of health (and, likewise time). Their health decreases steadily as they play, but also each time they take damage from an enemy. Players may eat food to increase their health or insert another credit to buy more health, and thereby gain more time.

Implementation

In order to implement a time limit, a game designer needs a clock of some sort to keep time, and a mechanism for measuring the value of the clock. If the game is meant to automatically do something when the clock reaches a specific value, it also needs a way to trigger an event as well as a way of resetting the clock. Over the years, game designers have implemented timers in a number of different ways.

Mechanical

A sand timer is common in board games.

There are plenty of purely mechanical ways to keep time. Board games often use cheap hourglass-like sand timers, but they can also incorporate traditional spring and gear mechanism clocks like those used in chess. These are usually manually started and watched by the players to know when the time reaches its limit. Clocks of this nature can also be automated by adding additional mechanisms to them, however, purely mechanical timer systems like this are often not very accurate, difficult to calibrate, wear out over time, and are susceptible to changes in their environment like the temperature or humidity.

Although mechanical clocks worked well enough for the games of their time, most are being converted to electric clocks.

Electro-mechanical

An electro-mechanical timer.

Electro-mechanical timers are usually built on a motor attached to a gear train which is configured in a specific manner to keep time. To automate them, they can be designed to turn a cam to switch an electric circuit open to start the game, then closed to stop the game when the time limit is reached. Electro-mechanical timers have to be initially set and adjusted manually and, while they are much easier to automate in an electrical game than a than purely mechanical clock, they are still susceptible to environmental changes and breakdown over time. They too have mostly been replaced by electric clocks.

Electric

The timing crystal on an Atari 2600.

When physicists discovered that passing an electric current through certain crystals caused them to vibrate at very precise rates, clocks were made based on them. Clocks with quartz timing crystals are extremely accurate and stable, and act as the "heartbeat" of an electronic system like a computer or video game console. However, due to their nature, timing crystals are much more difficult to implement. Once they're wired into a system's hardware, programming often goes through multiple levels of complexity to make them useful for a game.

For example, if a game programmer wanted to make a game for the Atari 2600 with a time limit, they would have to program this based on the console's crystal timer. The Atari's timing crystal vibrates 3,579,575 times a second (each vibration is referred to as a "clock cycle"). Clock cycles are often abbreviated and written in hertz (Hz), so the clock of the Atari 2600 runs at 3.58 MHz. However, the system only processes a CPU instruction every third clock cycle, which means the processor of the Atari only runs at 1.19 MHz. So, to have a time limit of 60 seconds, the programmer would have to wait until 71,591,460 clock cycles passed (that's 1,193,191 per second for 60 seconds). However, the programmer can't just make the CPU count clock cycles, it also has to perform all the necessary tasks to run the game, which means keeping track of how many clock cycles each operation takes and subtracting them from the total number. Trying to keep track of how many cycles have passed, while at the same time processing the game, was a very difficult task for programmers on early hardware, so later manufacturers introduced hardware interrupts which kept track of some of the timing automatically. Subsequent firmware and operating systems fully automated the timing process, so, on computers and video game consoles today, it's very easy to measure timing at extremely precise intervals using software alone.

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