Understanding the Internet

• Mainframes and Terminals: The first electronic computers filled whole rooms. Programmers interacted with them by inserting “punch cards” that displayed holes in designated positions, and data was stored on large rolls of magnetic tape. As the technology advanced, computers could serve several operators at once. A mainframe computer would be connected to many user stations, called terminals, each with its own keyboard and screen.
• Servers and Clients: When personal computers were developed, people began to connect them in a similar way. One PC would act as a server, and the others would connect to it as clients. Nowadays, a personal computer can act as a media server for other devices, such as your television. And a distant computer can act as a server to deliver a Web page to your personal computer, the client.
• LANs, WANs, and WLANs: As more advanced computing devices were developed, home and office networks were established. LANs (Local Area Networks), which served a single office or home, and the larger WANs (Wide Area Networks) both used physical connections. Later, wireless technology allowed for WLANs (Wireless Local Area Networks). Your school or home may provide both LAN and WLAN connections.
• Modems and Routers: Short for “modulator-demodulator,” a modem is a device that can connect to the Internet. A router is a stand-alone device used to network multiple computing devices in one location, by Ethernet cable or wirelessly. Most often, a router is also connected to a modem to provide Internet connection to devices on its network.
• ISPs: An ISP (Internet service provider) is a company that sells Internet access. Common connection types include the following:
  • Dial-Up is a slow connection using a normal telephone line. While the computer is connected to the Internet, the line cannot be used for phone calls.
  • DSL (digital subscriber line) uses a dedicated telephone line (or sometimes a pair) to provide a faster, always-on connection to the Internet. It works well for users within one mile of the service provider but weakens at greater distances.
  • Cable uses heavy-gauge copper wires or even fiber-optic lines to deliver high-speed access over greater distances.
  • Satellite provides Internet access from a satellite orbiting the earth to a receiving dish at the user’s location. Download speeds (receiving data from the satellite) can be nearly as good as DSL or cable, but upload speeds (sending data to the satellite) are much slower.
  • T1 and above are high-speed connections typically offered only to businesses.

• DNS: Every device on every network has its own unique numerical address. A router within a home network is often at 192.168.1.1, and it might assign 192.168.1.4 to one computer, 192.168.1.20 to another, and so on. Addresses on the Internet are assigned a similar numerical code. To make things easier for humans, these numbers are mapped in DNS (Domain Name System) servers to names like www.google.com or www.nasa.gov. When you send an email or access a Web page, a DNS server translates that address to its number code for computers to use.
• Ethernet: Ethernet cables look like phone lines but are slightly larger. They are generally used for high-speed connection within a local network.
• Bluetooth, Wi-Fi, and Mobile Telephony: These connection types use wireless modems to send and receive radio waves. Bluetooth is a short-range connection—about 10 meters (32 feet)—commonly used to connect a computer to peripherals like headphones, a keyboard, and a mouse. Wi-Fi (Wireless Fidelity) has a longer range—about 20 meters (65 feet)—and is the basis of WLAN networks (see previous page). Mobile telephony connects cell phones to towers wirelessly.
• VOIP Telephony: VOIP (Voice Over Internet Protocol) is a technology for making free or low-cost phone calls over an Internet connection.
• World Wide Web: The World Wide Web is a collection of files interconnected by clickable links and viewed as pages in a browser program. Those pages may contain text, images, and even audio or video files. Although many people use the terms Web, World Wide Web, Internet, and Net interchangeably, the Web is only part of the Net. (Also see “Deep Web” on page 391.)
• The Cloud: As computing becomes increasingly portable and people use different devices to connect at work, at home, and elsewhere, the idea of storing files online in “the Cloud” has grown popular. This makes files accessible from anywhere with an Internet connection. Also, in “Cloud Computing,” server computers do the more complex processing, allowing portable computers to run “thin client” software.

Example Home Network

This graphic shows how various devices might communicate within a home network, using technologies described above. This graphic shows how various devices might communicate within a home network, using technologies described above.