Personal computers (PCs) had been manufactured since 1977, but the market for them did not come of age until 1981, when IBM produced its first one. IBM's size enabled it to market its PCs aggressively, and sales climbed in three years from 25,000 to 3 million, although its experiment with a low-cost model, the PCjr., failed. The Apple Corporation, famous for development of the Apple II, introduced the Macintosh in 1984. By 1987 its Macintosh II and SE models were the most powerful personal computers on the market. The Mac was also regarded as more user-friendly than personal computers with "disk operating systems," and debates over Mac versus DOS continued for years. The Mac's "mouse" for moving the cursor on the screen made it even more user-friendly, and eventually other lines of computers also made the mouse a standard feature.
Sales of personal computers stood at 1.4 million in 1981. Sales doubled in 1982, on their way to 10 million in 1988, at a cost then of $22 billion. A number of other computer developments made news that year. One was the "virus," a mischievous small program planted in an operating system with the intent of altering or deleting data throughout the network as the virus spreads. Another was the expanded capacity and speed of laptop computers, with sales exceeding $1 million. A third concerned possible health hazards posed by computer monitors, known as video display terminals. Studies showed that many people who worked at monitors for six hours or more each day developed difficulties in