Metaphors have a powerful role to play in helping us make sense of our world. According to Gerald Zaltman, "they help us see new connections, interpret our experiences, and draw meaning from those experiences." [1] He points out that we use almost six metaphors per minute of spoken language. Just as they permeate everyday life, so metaphors also permeate human-computer interfaces.

Metaphors are the representation of one thing in terms of another. Complex user interfaces can be more easily understood if they are depicted in terms of some commonplace system that users are familiar with. Like the humble desktop metaphor, which is the "single most important design decision of the last half century." [2]

The desktop concept was invented in 70s by a group of researchers at Xerox’s high-end computer science lab in Palo Alto. Originally multiple windows used to compete for space on a screen that wasn’t much bigger than a sheet of paper. The breakthrough came when a researcher named Alan Kay began thinking of the screen as a desktop. "People in offices got around the same problem of too much paper and not enough room by piling pages on top of one another." [3] Kay simply transferred this real world solution to the computer and overlapping windows were born. No-one looked back from there.

Part of the reason for the staying power of this particular interface metaphor was that it was extendible. It is not a huge mental leap to incorporate other familiar office concepts such as a trash can and files.

Of course, like with most things, the use of metaphors can go too far. It’s easy to imagine the desktop metaphor being taken too literally, with piles of unordered paper, scattered business cards and coffee mug stains. That’s the beauty of the metaphor, it can be used to help understanding without being tied down by the limitations of the real-world equivalent.

(For those interested in the history of the modern PC user interface, I would strongly recommend reading Dealers of Lightning, the story of the Xerox PARC lab. It’s a very interesting account of the invention of the first personal computer and graphical interface.)

[1] From How Customers Think by Gerald Zaltman
[2] Interface Culture by Steven Johnson
[3] From Dealers of Lightning by Michael A. Hiltzik

- Trent