Have you ever wondered what's going on when you click your mouse on some underlined text in a browser window and suddenly the screen fills with text and graphics that clearly come from some other faraway place? It's as if you've been transported to another location, as if a window has opened up on another world. If you're on a fast cable or DSL (“digital subscriber line”, the first of many acronyms in this chapter) connection, the transformation is almost instantaneous; if you're using a slow modem, then updating the screen can take several seconds or even minutes, but in any case the behind-the-scenes machinations making this transformation possible leave little evidence. Occasionally, however, you'll catch fleeting glimpses of the machinery through little cracks in the user interface.
If you use a dial-up connection and modem to connect with your Internet service provider, you may hear an awful squawking as your modem and the service provider's modem initiate two-way communication. Similar noisy exchanges can occur when one fax machine attempts to communicate with a second. In both cases, computer programs at each end of a telephone connection are validating, handshaking, synchronizing and otherwise handling the transmission of information. As smarter modems and fax machines replace older technology, these noisy accompaniments are being silenced, since a human need no longer overhear them to check that things are proceeding as desired.