What exactly is an interface anyway? In its simplest sense, the word refers to software that shapes the interaction between user and computer. The interface serves as a kind of translator, mediating between the two parties, making one sensible to the other. In other words, the relationship governed by the interface is a semantic one, characterized by meaning and expression rather than physical force. Digital computers are “literary machines,” as hypertext guru Ted Nelson calls them. They work with signs and symbols, although this language, in its most elemental form, is almost impossible to understand. A computer thinks—if thinking is the right word for it—in tiny pulses of electricity, representing either an “on” or an “off” state, a zero or a one. Humans think in words, concepts, images, sounds, associations. A computer that does nothing but manipulate sequences of zeros and ones is nothing but an but an exceptionally inefficient adding machine. For the magic of the digital revolution to take place, a computer must also represent itself to the user, in a language that the user understands.
Representing all that information is going to require a new visual language, as complex and meaningful as the great metropolitan narratives of the nineteenth-century novel.
Put simply, the importance of interface design revolves around this apparent paradox: we live in a society that is increasingly shaped by events in cyberspace, and yet cyberspace remains, for all practical purposes, invisible, outside our perceptual grasp. Our only access to this parallel universe of zeros and ones runs through the conduit of the computer interface, which means that the most dynamic and innovative region of the modern world reveals itself only through the anonymous middlemen of interface design.
[Quote adapted from Johnson, S. (1997) Interface Culture. Harper Collins (pp.14-19).]