Back in the 1990s, almost all residential users accessed the Internet over ordinary analog telephone lines using a dial-up modem. Today, numerous users in underdeveloped countries and in rural areas in developed countries (where broadband access is unavailable) still access the Internet via dial-up. In reality, it is estimated that 10% of residential users in the United States used dial-up in 2008 [Pew 2008].
The tern "dial-up" is used because the user's software actually dials an ISP's phone number and makes a traditional phone connection with the ISP (e.g., with AOL). As shown in the following figure, the PC is attached to a dial-up modem, which is in turn attached to the home's analog phone line. This analog phone line is made of twisted-pair copper wire and is the same telephone line used to make ordinary phone calls. The home modem converts the digital output of the PC into an analog format suitable for transmission over the analog phone line. At the other end of the connection, a modem in the ISP converts the analog signal back into digital form for input to the ISP's router.
Dial-up Internet access has two major disadvantages. First and foremost, it is painfully slow, providing a maximum rate of 56 kbps. At a 56 kbps, it takes about eight minutes to download a single three-minute MP3 song and many days to download a 1Gbyte movie! Second, dial-up modem access ties up a user's ordinary phone line - while one family member uses a dial-up modem to surf the Web, other family members cannot receive and make ordinary phone calls over the phone line.