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When using a headset with a PC, one needs to connect it to two 3.5mm jacks, one for the audio output and one for the mic.
But, when using a USB headset, only one connector serves both the purposes.
Also, on most phones and laptops, one 3.5mm jack serves both the purposes as well.

I'm not sure if the 3.5mm jack doesn't have the ability to do both at once or if two different ports are made by PC manufacturers on purpose.

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    There doesn't seem to be a question here.... to answer the mobile phone 3.5mm port... a phone port typically makes use of a 3.5mm jack that has an additional ring for the microphone and remote control signals (volume up/down etc.). A typical 3.5mm audio jack doesn't have the microphone ring, thus can only be used for audio. Cables are available that can combine a headset with separate audio in/out to a single 4 ring jack: images-na.ssl-images-amazon.com/images/I/…
    – Kinnectus
    Sep 5, 2018 at 11:59

1 Answer 1

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Welcome to Superuser )

There are different types of 3.5mm jacks.

  • 2-pin connectors exist for mono audio but one rarely comes across them these days
  • 3-pin connectors carry stereo audio in only one direction (in OR out)
  • 4-pin connectors exist for stereo out with one extra contact for microphone

Each jack plug need to be used in combination with the correct socket. Image below for illustration purpose only. It does not cover all possible layouts:

enter image description here

To make it more complicated there are different ways 4-pole jacks are wired between different equipment manufacturers. But this is the whole another story...

Answering your original question, it is probably the case that your PC manufacturer has equipped your machine with two separate ports for microphone and audio out. One can only speculate about the reasons why the PC was designed like that. Could have been any of the following:

  • Manufacturing cost
  • Compatibility with standard headphones
  • Compatibility with standard speakers as pointed out by @Randy Orrison
  • Combination of the above
  • Something else...

Comparing with USB is not strictly correct. First of all USB is a digital interface while 3.5 mm jack is analogue. Having that said, USB can carry multiple signals across the same wire. Also if you look closer at USB connector (type A most commonly found on PCs) you will see that there are 4 contacts inside...

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    In my experience it's more common to have speakers, and less commonly a separate microphone, and headsets are even less common - so it makes sense to have separate jacks which can handle all configurations. Sep 5, 2018 at 12:14
  • It's probably also worth touching on the fact that USB headsets actually present to the system as a separate sound-card, so they only need the connection for that, and not for each speaker and mic. Sep 5, 2018 at 18:40

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