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Modem The most familiar example of a modem turns the digital '1s and 0s' of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone System (POTS), and once received on the other side, converts those sounds back into 1s and 0s. Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps". Far more exotic modems are used by internet users every day. In telecommunications, "radio modems" transmit repeating frames of data at very high data rates over microwave radio links. Some microwave modems transmit more than a hundred million bits per second. Optical modems transmit data over optic fibers. Most intercontinental data links now use optic modems transmitting over undersea optical fibers. Optic modems usually use interferometer filters called etalons to separate different colors of light, and then individually turn the pulses of each color of light into electronic digital data streams. Optical modems routinely have data rates in excess of a billion (1x109) bits per second. Their bandwidths are currently limited by the thermal expansion of the etalons; heat changes an etalon's size and thus its frequency. Winmodem A Winmodem or Softmodem is a stripped-down modem for Windows that replaces tasks traditionally handled in hardware with software. In this case the computer's built-in sound hardware is used to generate the tones normally handled by the analog portion of the modem. A small piece of hardware is then used to connect the sound hardware to the phone line. Modern computers often include a very simple card slot, the Communications and Networking Riser slot (CNR), to lower the cost of connecting it up. The CNR slot includes pins for sound, power and basic signalling, instead of the more expensive PCI slot normally used. Winmodems are often cheaper than traditional modems, since they have fewer hardware components. One downside of a Winmodem is that the software generating the modem tones is not that simple, and the performance of the computer as a whole often suffers when it is being used. For online gaming this can be a real concern. Another problem with WinModems is lack of flexibility, due to their strong tie to the underlying operating system. A given Winmodem might not be supported by other operating systems (such as Linux), because their manufacturers may neither support the other operating system nor provide enough technical data to create an equivalent driver. A Winmodem might not even work (or work well) with a later version of Microsoft Windows, if its driver turns out to be incompatible with that later version of the operating system. Broadband ADSL modems, a more recent development, are not limited to the telephone's "voiceband" audio frequencies. Some ADSL modems use coded orthogonal frequency division modulation. Cable modems use a range of frequencies originally intended to carry RF television channels. Multiple cable modems attached to a single cable can use the same frequency band, using a low-level media access protocol to allow them to work together within the same channel. Typically, 'up' and 'down' signals are kept separate using frequency division multiplexing. Broadband modems should still be classed as modems, since they do utilise analog/digital conversion. They are more advanced devices than traditional telephone modems as they are capable of modulating/demodulating hundreds of channels simultaneously. Many broadband "modems" include the functions of a router and other features such as DHCP, NAT and firewall features. When broadband technology was introduced, networking and routers were not very familiar to most people. However, many people knew what a modem was as most internet access was through dialup. Due to this familiarity, companies started selling broadband adapters using the familiar term "modem".
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