I am writing this essay on a Macintosh computer, a machine that replaces the gears and levers of a typewriter with a microprocessor, electronic circuitry, software, and a display screen. On the floor is a modem, which lets my computer talk to other computers over the phone lines. There are more than 30 million people on the Internet whom I could reach via modem if I knew their electronic- mail address. I check my E-mail; I'm carrying on several electronic conversations about this essay, and about other topics. I check a few bulletin boards ( ....