The device used to make a dial up connection is called a modem. The word "modem" is a contraction of the words modulator and demodulator. A modem sends and receives data over a phone line. The modem has two main functions. While sending data, it modulates the data into a signal that is compatible with the phone line, i.e. an analog signal. While receiving data, it demodulates the analog signal received over the phone line back into digital data.

Modems came into existence in the 1960s. They were used to make dial up connection by the individual terminals to connect through a network to a central computer over the phone lines. The 1960s were the age of time shared computers. Hence, a business could buy computer time from a time share facility to connect to its terminal. They used modems with the speed of 300 bit per second (bps). In a system configuration existed at that time, a remote dumb terminal could dial in to a large, central computer through a 300 bps modem.

Here, it is important to understand that a dumb terminal is simply a keyboard and a screen. In that time, the DEC VT-100 were very commonly used and popular dumb terminals. They had become a standard of the day. The VT-100 could display 25 lines of 80 characters each. When the user typed a character on the terminal, the modem sent the ASCII code for the character to the computer. The computer then sent the character back to the computer so it would appear on the screen.

300 bps modems were popular in 1960’s and 1970’s. The reason for that is that is that the speed was good enough at 300 bps as it could transmit at almost 30 times faster than a person can type or read. When personal computers started appearing in the late 1970s, bulletin board systems (BBS) became highly popular. A person would set up a computer with some BBS software and a modem and other people would dial in to connect to the bulletin board. This result inn increase in the data transfer over the connection. With the arrival of internet and GUI, the images were also started flowing through the connections.

Once people started transferring large programs and images to and from bulletin board systems, however, 300 bps became intolerable. Hence, various companies started coming out with faster modems over next 15 years. Modems went through a series of steps in evaluation in 1980’s and 1990’s.

1200 bps and 2400 bps modems were in use in 1980’s. By the end of 1990, 9600 bps modems came in use. 33.6 Kbps modems became the standard in mid 1990’s. They were the mostly used modems thought 1990’s. The most important step in evaluation of modem came in 1998-99 when 56 Kbps Modem came in to picture. Today they are the most commonly used dial up modems. Also, many more versions of modems like cable modems and wireless modems are in use. Modems are getting faster and more sophisticated with time.

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