Dial-up Internet access is a type of Internet connectivity that operates through a standard telephone line. By running the telephone line to a modem device in the personal computer, and configuring the computer to dial a specific phone number, the computer is granted Internet access.

Dial-up Internet access is offered through a number of Internet service providers (ISPs). Most ISPs lease a set of telephone numbers, sometimes local, sometimes national, that dial into network pipelines that feed into the Internet. Subscribers to the ISP normally pay a monthly or yearly fee. For this fee, the subscriber can access the Internet any time of the day or night to cruise the World Wide Web, send and receive email, participate in IRC chat rooms and USENET newsgroups.

Before a person can subscribe to a dial-up service, he or she must have a computer and dial-up modem. A modem is an inexpensive component that fits into a free slot inside the computer. There are also external modems that sit alongside the computer, connected to the computer by a serial or alternate type cable. A telephone line feeds into the modem.

The modem is controlled by software in the computer; for example, the Network Connections utility that comes with Microsoft Windows operating systems. Here you can setup a profile for the ISP, which will tell the modem what phone number to call and how to communicate with the dial-up service. The ISP itself provides this information.

Upon joining a dial-up service, the subscriber chooses a username and password. Once the modem calls the phone number and makes a connection, a "handshake" takes place in which information is exchanged between the computer modem and the remote server. The username and password is supplied by the modem. This grants the user access through the dial-up gateway to the Internet.

Dial-up service is the least expensive but also the slowest type of Internet access. Due to the limited bandwidth - the ability for the modem to send and receive data - dial-up service can take up to five minutes to download just one megabyte of data. Caching frequently visited pages, and other software tricks and tweaks can speed up the experience of dial-up access in some cases. However, if your main purpose online is multimedia-centric, (music, movies, and graphic-laden websites), dial-up service may be so slow as to be unsatisfactory.

Faster Internet options include, most commonly, cable and DSL (Digital Subscriber Line or Dedicated Service Line). DSL uses your standard telephone line for fast Internet access, but differs from dial-up in that DSL uses a digital frequency. Dial-up transmits data across the telephone line using the standard analog frequency, making it impossible to use your telephone while online. With DSL service you can be online and use the telephone at the same time. Cable differs from dial-up in that Internet access is provided via the same cable company that brings cable television into the home.

Both cable and DSL provide a 24/7 Internet connection, allowing for subscribers to leave the computer actively connected to the Internet 24 hours a day. These services are more than 30x faster than dial-up, however, they are also more expensive. Exceptions might be dial-up services that charge more than $15-20 (US dollars) per month. In this case you may be able to find high-speed Internet access in your area at a comparable price.