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The game port is the traditional connector for video game input devices on x86-based PCs. The game port is usually integrated with a PC I/O or sound card, either ISA or PCI, or as an on-board feature of some motherboards. more...

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Microsoft has discontinued game port support with Windows Vista, so it is probable that manufacturers will cease to produce boards with this connector. However, it's still entirely possible to provide third-party drivers that will work with the gameport.

Gameport details

Analog interface

Unlike most other joystick connectors (and controllers) during the early days of home computing and game consoles, the game port is actually analog rather than digital, relying on some form of ADC to interpret joystick movements. Early IBM-PC manuals describe this port as suitable for connecting two analog paddles rather than joysticks. This approach has historically given the IBM-PC an advantage in simulation games, especially flight simulators, but on the other hand, rendered the design and use of simpler arcade or console joysticks more complex and needlessly convoluted, apart from being essentially incompatible with any existing joystick interface, most notably the standard DE-9 connector Atari joysticks.

Acquisition and programming

Also, while other joystick standards (such as Atari or NES joysticks) are very easy and straightforward to use by programmers, the game port requires careful programming and well-timed software interrupt triggering in order to read an input. This of course caused performance issues as reading the game port took a notable amount of CPU time, especially compared to systems with a 'normal' digital (TTL) joystick port.

Circuits

The typical implementation of a gameport uses a capacitor and a simple voltage comparator, which together form a sort of crude ramp-compare ADC, which needs to be periodically polled and reset at precise moments in order to read an input, something that needs to be done several times (generally above 30) per second in order to provide a responsive game input, and the actual acquisition frequency and value typically depend on the joystick's internal resistance, noise, CPU speed and the total joystick-capacitor's RC time constant.

Known issues

Its analog nature has also been the cause of many problems e.g. all kinds of joysticks needed "calibration", even arcade-style ones since no game controller and no joystick produced the same measurements each time, but they were dependent on the exact way acquisition was made and even by the CPU's speed in some rather poor designs. Also, all kinds of PC Gameports suffer from electrical noise.

Read more at Wikipedia.org