Interface is the point of change.
The interface between the ocean and the atmosphere is the surface of the water. It is where the two meet.
Interface in computer or HCI terms is where information or control moves from one realm to another. When this happens, a change or translation is necessary and unavoidable.
CONTROL INTERFACE Take a simple kitchen knife. The useful part of the knife is the cutting edge of the blade. In order for us to to use the blade however, the handle is added. When you use the knife, the control you exercise through your hand is translated to moved to the blade through the handle. Different shaped handles allow you to use the knife in different ways.
It is the same with a door handle. You use the handle to 'operate' the door. Some door handles are simple and convenient, others confusing and some even dangerous,, like the spherical handles which you will burn your hand trying to operate if you are in a room that's on fire, there is not way you can apply force to the handle without gripping it with your hand.
INFORMATION INTERFACE There is also the interface when information moves from one domain to another. The term domain it is intended to highlight that information which stays in the same medium/domain does not go through an interface, such as digital data which travels for miles down a cable. It is still the same.
Information changes when it moves from a photograph to your brain, through your eyes. It is processed and not passively received. Not that it would be beneficial it was, or even if such a thing would be possible. When you print a photograph, the original image which has been captured on film changes yet again when it 'reaches' the photosensitive paper.
COMPUTER INTERFACE We don't interface with computers, we interface through computers.
The whole point of having an interface is that we cannot directly access, manipulate or distribute information through the computer.
This is both a barrier and an opportunity.
Computers do not allow us to interact in ways we have previously thought of as being direct, such as by using our hands touching objects and manipulating them.
However, we can use the powerful and flexible intermediary computers are to extend the possibilities of our interaction in ways we could never do if we were to follow the traditional physical route and stay limited by our immediate sensory reach.
HUMAN COMPUTER INTERFACE Human-Computer-Interaction is the discipline which studies and works towards augmenting human (primarily cognitive) capabilities (as individuals as well as groups), focusing on efficient interfaces, through computer systems and computer networks, which the user interacts with information, people, control and the users own thoughts.
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