A 3.5mm headphone jack, sometimes called a 1/8-inch headphone jack by American users, is a versatile jack found in many modern electronics. While specified as a headphone jack, the 3.5mm headphone jack is able to perform a variety of different operations. This jack can be used to transfer video when used with camcorders and smartphones, and to hook up game systems to a TV. Amateur radios use this jack as a speaker-microphone, and some microphone units for musicians use this input. While not as popular as a universal serial bus (USB) port, this jack also is used to transfer data with some devices.
Mostly commonly, the 3.5mm headphone jack is used for headphones and earbuds. If someone is using headphones to listen to audio from a computer, a miniature music player, early compact disc (CD) or cassette tape player, or nearly any other device that plays audio, a 3.5mm jack is likely being used. The only exception is mobile phones, which commonly use 2.5mm jacks. A 3.5mm jack is able to create either mono or stereo sound, depending on the audio source.
When a camcorder or smartphone records video, it needs to output that video to make it watchable on a TV. Direct output methods commonly use a 3.5mm headphone jack, because the jack is able to output both sound and video. Depending on the cable, there will either be mono or stereo sound outputted. These same cables are used to connect digital video disc (DVD) players and many game systems for TV use and to connect stereos to large audio players.
Along with transferring sound, a 3.5mm headphone jack also can be used as an audio input. In this arena, mostly amateur radio operators use this jack; some mobile phones also use this to carry audio. Early microphones, and some modern versions, for musicians use the 3.5mm jack. These are used mostly to record onto cassette tape with mono sound, but some are able to record to CDs or to input the sound into a computer.
Data transfer is common for many devices, because they hold pictures, files and other documents that need to go from the device to a larger computer. The most commonly used jack here is a USB port, because it is more versatile for this, especially with computers. While USB is more popular, the 3.5mm headphone jack is used with some devices, the most common being graphing calculators and some amateur radios.