Networking is one of the most important trends in computing today. Computer networks are growing in popularity because they allow computers to share hardware and to send software and data back and forth. In addition, networks enable people to work together in ways that would be difficult or impossible without them.

LANs are made up of computers that are close enough to be directly connected with cables or wireless radio transmitters/ receivers. Most LANs include shared printers and file servers. WANs are made up of computers separated by a considerable distance. The computers are connected to each other through the telephone network, which includes cables, microwave transmission towers, and communication satellites. Many computer networks are connected together through the Internet so messages and data can pass back and forth among them. Some specialized networks, such as global positioning systems and financial systems, serve unique functions.

Most computer networks today use the Ethernet architecture; an Ethernet port is a standard feature on most modern PCs. Computers can be directly connected to networks through Ethernet ports. When high-speed direct connections aren’t possible, a PC can transmit and receive signals over standard phone lines with a modem. The modem converts the PC’s digital signals to analog so they can travel through standard phone lines. Broadband connections offer much more bandwidth than standard modem connections do, so they can transmit large amounts of information more quickly. These connections include DSL, which uses standard phone lines; cable modems, which use cable TV lines; satellite, which uses TV satellite dishes; and Wi-Fi, which uses short-range wireless 802.11 transmitters. Wi-Fi is a type of wireless network technology that’s exploding in popularity because of its potential for providing universal Internet access. All of these technologies offer connections to Internet backbones, many of which transmit astronomical amounts of data quickly through fiber-optic cables.

Communication software takes care of the details of communication between machines—details such as protocols that determine how signals will be sent and received. Network operating systems typically handle the mechanics of LAN communication. Many popular PC operating systems include peer-to-peer networking software, so any PC or Mac on a network can serve as a server as well as a client. Terminal programs enable personal computers to function as character-based terminals when connected to other PCs or to timesharing computers. Other types of specialized client programs have graphical user interfaces and additional functionality. Timesharing operating systems enable multiuser computers to communicate with several terminals at a time.

Email, instant messaging, and teleconferencing are the most common forms of communication between people on computer networks. They offer many advantages over traditional mail and telephone communication and can shorten or eliminate many meetings. Because of several important limitations, however, email and teleconferencing cannot completely replace older communication media. People who communicate with these new media should follow simple rules of "netiquette” and exercise a degree of caution to avoid many of the most common problems.

Peer-to-peer computing was popularized by music-sharing services, but its applications go beyond music sharing. Many businesses are exploring ways to apply P2P technology. Grid computing goes beyond P2P computing by enabling people to share processor power with others. Some organizations are working to build a grid-computing model that would make the Internet work like a shared utility. Many see this as a big step toward cloud computing— treating the Internet as a cloud containing shared software and hardware whose physical location isn’t particularly important.