Today's technology scene seems overheated to some. Apple is the most valuable company on earth. Software apps are reaching tens of millions of users within weeks. Major technology names like Research in Motion and Nokia are being undone by rapid changes to their markets. Underlying these developments: the unprecedented speed at which mobile computers are spreading.

Presented below is the U.S. market penetration achieved by nine technologies since 1876, the year Alexander Graham Bell patented the telephone. Penetration rates have been organized to show three phases of a technology's spread: traction, maturity, and saturation.

Those technologies with "last mile" problems—bringing electricity cables or telephone wire to individual homes—appear to spread more slowly. It took almost a century for landline phones to reach saturation, or the point at which new demand falls off. Mobile phones, by contrast, achieved saturation in just 20 years. Smart phones are on track to halve that rate yet again, and tablets could move still faster, setting consecutive records for speed to market saturation in the United States.