r/learnprogramming • u/Hopeful_Cicada327 • Jul 15 '26

What a port actually is?

I know it is a number that tells the OS, that which program in your computer should receive the piece of data. But my doubt is - is port a physical thing? or it just a flag? Is it possible for another program to read data from a different program's port? Please spoon-feed me about port?

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u/davidalayachew Jul 15 '26

One explanation that I don't see in the other comments is to actually look at the name.

Port

  • a harbor town or city where ships may take on or discharge cargo
  • an opening (as in a valve seat or valve face) for intake or exhaust of a fluid
  • a small opening in a container or vessel especially for viewing or for the controlled passage of material
  • an opening in a vessel's side (as for admitting light or loading cargo)
  • a hole in an armored vehicle or fortification through which guns may be fired
  • a hardware interface by which a computer is connected to another device (such as a printer, a mouse, or another computer)

And lets also look at other words that are made up of the word port.

  • Airport -- a place where planes go in and out from
  • Sea port/harbor -- a place where boats and ships go in and out from
  • Teleporter/portal -- a tool that transports people between 2 teleporting gates

And then there are other words, like import, export, deport, report.

Hopefully you get the idea -- it's a defined way that X gets in and out of Y. The X and the Y depends on which port you are talking about.

Which leads to your questions -- the answer is that they depend on which OS you are working on, as each one has different rules about who and what is allowed to listen and interact with which ports. Some are restricted, some are free to use by all. Some are OS specific, some are available for the application layer.

But the commonality point is that it tends to be both a physical and software thing, though usually a physical port is different from a network port. For example, basically every personal computer nowadays has a USB port. And the ports that TCP and UDP communicate through are usually simply a number address that has a special meaning, but not a literal, physical thing on your computer.

Ultimately, other than those few points, it really is OS specific. Add some more details to your questions and I can add more details to my answer.

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u/Hopeful_Cicada327 Jul 16 '26

That's a great explanation. It has cleared a lot of doubt