Apple just released the Macbook Wheel, a computer with only a single input device. Well, it actually has multiple inputs – an entire scroll wheel, plus a button in the middle.
But it’s not that ridiculous of an idea. In Beautiful Code, there’s a chapter about how some researchers needed to design software for parapalegics (like Stephen Hawking). They had the most restrictive user interface possible: a single input button. In fact, it was a breakthrough when the researchers realized that the user could potentially hold down the button for variable lengths of time:
From observing Professor Hawking use Equalizer, I discovered a new mode of operation: besides simply just clicking the button, he could hold down the button and release it at a strategic moment. The button, in effect, is not merely a binary input device, but actually an analog one, for it can provide a signal of varying duration. We thought long and hard about how best to use this new power we were presented with: we could now get more information out of a click than a simple bit. We could, for instance, allow the user to pick from a list of choices. A short click would now be used for the default action, while a long click opened up many other options.
Crazy! It is a testament to the skill of Hawking and the engineers that they were able to get typing speed up to a reasonable pace.
Here’s some of the pages from the book. You’ll need to buy it to read the whole chapter (which I highly recommend).