Computer technology dated from World War II; by 1970 giant IBM mainframe computers were well-known (see Chapter 27). The size and cost of these computers made them practical only for big corporations or government agencies such as the Pentagon and the Census Bureau. Even the smaller minicomputers built by Seattle's Digital Equipment Corporation (DEC) were far too bulky and expensive for individual use.

An exciting new entrant, the personal computer, loomed on the horizon. With the development of silicon-chip transistors and integrated circuits in the late 1950s, the data that could be implanted in a single chip increased enormously. "Moore's Law," proclaimed in 1965 by Gordon Moore, founder of Intel, a computer-chip manufacturer, held that silicon chips' capacity would double every eighteen months. The prediction proved remarkably accurate. With silicon chips, computers could be miniaturized and still match the mainframes' capacity.

Unlike the inventions that had once emerged from Thomas Edison's New Jersey laboratory, the personal computer did not spring from a single research project, but rather from many young hobbyists working at home and hovering around the margins of the industry. In the late 1960s, for example, Seattle high-school students Bill Gates and Paul Allen biked daily to the offices of DEC, where company officials let them tinker with computers in exchange for finding flaws (or "bugs") in the instructional programs (called software) that enabled DEC's computers to perform useful functions. "We were called computer nerds," Gates recalled. "Anyone who spends their life on a computer is pretty unusual." In 1972 Gates and Allen, still teenagers, formed Traf-O-Data, a programming company.

Meanwhile, the actual machinery, or hardware, of small computers evolved rapidly. In 1974 a struggling Albuquerque electronics company, Micro Instrumentation Telemetry Systems (MITS), developed a $397 do-it-yourself Altair computer kit using Intel chips. (The name Altair came from the TV show Star Trek.) When Popular Electronics magazine featured the Altair on its January 1975 cover, orders poured in.

The Altair appealed mainly to hobbyists. It had limited memory and primitive programming, and it was awkward to use, with levers rather than a keyboard. For home computers to be practical, better software was essential. Paul Allen, now working in Massachusetts, and Bill Gates, a Harvard freshman, volunteered to solve that problem. The Popular Electronics article caught their notice, and they offered to provide an operating system for the Altair by modifying BASIC, a program developed at Dartmouth College in 1964. MITS accepted, and Allen and Gates, changing their company name to Microsoft, moved to Albuquerque. MITS soon collapsed, and the Altair vanished, but the personal-computer era was underway.

Early home-computer enthusiasts valued cooperation and a casual, counterculture lifestyle. As one later recalled, "[We had our] genetic coding in the 60s, in the anti-establishment, anti-war, pro-freedom, anti-discipline attitudes." Groups of hobbyists such as the Homebrew Computer Club of San Francisco and New Jersey's Amateur Computer Group freely shared ideas, hardware, and software. In Cupertino, California, working in a garage, young Stephen Wozniak and Steven Jobs assembled a prototype small computer and soon began selling handmade models to friends.

As the personal computer's commercial potential became clear, this laid-back, cooperative attitude gave way to a competitive, proprietary business ethic. As early as 1976 Bill Gates, having reached the ripe old age of twenty-one, published "An Open Letter to Hobbyists," criticizing the free sharing (or "piracy") of software.

In 1976 Wozniak and Jobs began to sell their computers, called the Apple I, through the Byte Shop, a Bay Area computer store. The Apple II followed in 1977. The initial price of $666.66 soon dropped to $475. By 1980 sales hit $118 million. New marketing outlets quickly sprang up. The first ComputerShack opened in New Jersey in 1977. Radio Shack, Computerland, and other chains soon followed.

In the late 1970s IBM engineers working in Boca Raton, Florida, developed IBM's version of a personal computer. The IBM-PC hit the market in 1981. Priced at $1,565 it was far more expensive than the Apple II, but it bore the prestigious IBM name and boasted state-of-the-art hardware and Microsoft software.

Whether users chose Apple or IBM-PC, personal computers had an enormous cultural and economic impact. The sizzling industry fueled an economic boom that began in the mid-1980s and roared on into the 1990s. Youthful founders of start-up companies in "Silicon Valley" (a region south of San Francisco) amassed fortunes as investors bid up the prices of new stock offerings. (When recession hit in 2000, some of those fortunes evaporated.)

Bulky calculators, adding machines, and typewriters--the cutting-edge information technologies of earlier eras--gathered dust as people shifted to computer-based systems of data management, record-keeping, and word-processing. Popular in the home, personal computers also transformed office routines in businesses, hospitals, churches, and educational institutions. Secretaries who had spent their time filing, typing letters, and entering payroll and account records in ledger books now learned new computer-based skills. School typing classes gave way to computer instruction; library card catalogs to computerized databases. Library patrons were as likely to sit at a computer as to browse bookshelves. Computer games transformed juvenile leisure-time activities.

The possibilities seemed endless. "[I]f you're... thinking of buying [a personal computer]," proclaimed an industry publication in 1985, "you are only a few steps away from entering an expanding universe of incredible size and power." Further innovations came in the late 1980s and the 1990s: vastly enhanced memory capacity; ever-smaller laptop and hand-held models; microcomputers to control operating systems in automobiles and appliances; e-mail; and the Internet. The explosive growth of the Internet and the World Wide Web revolutionized the retrieval and transmission of information.

By 2000, 60 percent of U.S. homes had personal computers. Some cultural commentators worried about this fast-growing new technology. Would hours on the Internet cut users off from human contact? Would video games isolate the young from social interaction and blur the distinction between the real and the virtual? Others noted class differences in access to personal computers, as ownership spread much more slowly among blue-collar families and inner-city minorities than among the more educated and well-to-do.

Nevertheless, the personal computer was clearly here to stay. Only the future would reveal the full dimensions of the technological revolution launched in the 1970s by a handful of teenaged "computer nerds."