When IBM released the ThinkPad 701 subnotebook in 1995, users got a surprise. The unit was only 24.6 centimeters wide, but opening the lid presented a keyboard more than 4 centimeters wider. The secret was a dissection: The keyboard was stored in two pieces, each roughly a right triangle, and as the lid was opened these slid to either side, with one moving downward until they merged into a full-sized keyboard. (Mathematician Greg Frederickson wrote, “You find yourself opening and closing the lid repeatedly just to watch this movement!”)

The effect was so pleasing that the “butterfly keyboard” entered the permanent collection of Manhattan’s Museum of Modern Art, but IBM discontinued the feature when it retired the 701. Designer John Karidis said, “The butterfly keyboard was no longer necessary, because people moved to larger displays. Where the butterfly approach makes sense is where you want the largest keyboard possible in combination with an 8-inch or 10-inch display.”