Price dropped with size. In the early 1950s a transistor about as big as an eraser cost several dollars. By the mid-1970s, when transistors were approaching the size of a bacterium, they cost mere hundredths of a cent apiece. By the late 1990s the price of a single transistor was less than a hundred-thousandth of a cent—sometimes far less, mere billionths of a cent, depending on the type of chip.

Today's transistors come in a variety of designs and materials and are arrayed in circuits of many degrees of complexity. Some chips provide electronic memory, storing and retrieving binary data. Others are designed to execute particular tasks with maximum efficiency—manipulating audio signals or graphic images, for instance. Still others are general-purpose devices called microprocessors. Instead of being tailored for one job, they do whatever computational work is assigned to them by software instructions.

The first microprocessor was produced by Intel in 1971. Dubbed the 4004, it cost about $1,000 and was as powerful as ENIAC, the vacuum tube monster of the 1940s. Faster versions soon followed from Intel, and other companies came out with competing microprocessors, with prices dropping rapidly toward $100. The flexibility of the offerings had enormous appeal. If, for instance, the maker of a washing machine or camera wanted to put a chip in the product, it wasn't necessary to commission a special circuit design, await its development, and shoulder the expense of custom manufacturing. An inexpensive, off-the-shelf microprocessor, guided in its work by appropriate software, would often suffice. These devices, popularly known as a computer on a chip, quickly spread far and wide.

The creation of today's chips is a prodigious challenge. The design stage alone, mapping out the pathways for a forest of interconnected switches, may take months or even years and can be accomplished only with the help of powerful computers. Manufacturing is done in multibillion dollar plants of unearthly cleanliness, because a single particle of dust, boulderlike in the microworld of transistors, would ruin the circuitry. The tiny electronic creations wrought by all this engineering effort are now everywhere, operating behind the scenes in every household device and every mode of communication, transportation, recreation, and commerce.  Most extraordinary of all, the rate of advance shows no signs of slackening. Engineers and scientists are exploring three-dimensional architectures for circuits, seeking organic molecules that may be able to spontaneously assemble themselves into transistors and, on the misty edge of possibility, experimenting with mysterious quantum effects that might be harnessed for computation. Whether we are ready or not, computing power will continue its incredible expansion and change our future in ways yet unimagined.