This is a commonly used term especially when one wants to use any device or possibly determine what connections the device supports.
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Slowly you begin narrowing your understanding concerning this term to an interaction of at least two objects in which a given result must be given and in this case; a port and a cable or user and screen or user and program.
Discussing the operating system, I wrote explainning that it acts as a medium between the computer hardware and the application programs and user.
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Ones you have installed the operating system you can do some fundamental set up including coppying application programs on to the hard disk.
After which you now can begin interacting with your computer using application programs such as Microsoft office word, games, music players etc.
Therefore both operating system and application programs can be termed to be user interface.
a program that controls a display for the user and that allows a user to interact with the system.
Ports and peripheral devices
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This term also means a program adapted to work on a different platform other than that which it was designed for.
Going by the first definition; there are various ports on the system unit which serve specified purposes.
Each port is fit in with a respective cable which is used to transmit either data, power or both. There are various types of port interface on desktop computers.
Please read the detailed discos on port interface from here.
If asked to give a gist on port interface and peripheral devices, then I think what is right below this sentence could serve a good response.
Engineers have always and still are working out to make user friendly interfaces at all standards. User friendliness means; the ease for a user to use/ interact with her/ his device.