Winmodem

A Winmodem is a software modem designed to work with the Microsoft Windows operating system. A traditional modem uses hardware to perform its tasks, but Winmodems perform their key tasks with software. This makes them smaller and cheaper to produce, but it also means they cannot be easily used on other operating systems because the driver support requires far more effort to produce. In addition, they consume some of the CPU cycles on the computer to which they are attached, which can slow down application software on older computers. (They are sometimes referred to as a "port-on-a-stick.") Because they do so little by themselves, a computer program could use a Winmodem as something other than a modem; for example, it could emulate an answering machine.

Having most of the modulational functions delegated to software does serve to provide the advantage of easier upgradability to newer modem standards. although this is hardly an advantage as of 2005, with the latest V.92 56K protocol practically bearing the maximum achievable performance for a normal PSTN modem and telephone line and no significant plans future improvements/advancements seeming possible.

More commonly, winmodem drivers are usually enhanced in regards to their performance and to eliminate possible software bugs.

Winmodems have earned a certain notoriety for slowing down their computer systems and for having buggy drivers, although this reputation was largely garnered during the period of their introduction to the mass-market, whereupon they were oft to use substandard drivers, and be found in entry-level computers with slow CPUs. Any such reputation has not, however, halted their market popularity, and it is typical for any internal 56k-modem produced today to be a software-based modem.

Winmodems can be separated into two clear classes: controllerless modems and pure software modems. Controllerless modems, such as those made by Lucent and Motorola perform much of the modem work on the card, and require only small amounts of CPU power to complete. Pure software modems perform the entire emulation of a hardware modem on the main CPU, with Conexant's HCF and HSF standards being the most common.

Several times, the term "Winmodem" or "softmodem" is used in a largely derogatory manner, as opposed to hardware or "real" modems. The argument is that Winmodems and softmodems in general aren't real modems at all, but rather a simple electrical interface between computer and phone line, limiting itself to very basic functions such as voltage/current adaptation and functioning essentially as a DAC/ADC, much like a sound card which handles pure PCM and analog signals from and to the telephone line, while the host's CPU does the actual job of synthesizing or analyzing all necessary waveforms (carrier, dialing tones) and applying all necessary DSP techniques (FSK, QAM, PSK etc.) to a "virtual" signal, in order to encode and decode inbound or outbound data.

This essentially means that -at least the simpler- softmodems are nothing more than special purpose sound cards with mono DAC/ADC's and a telephone line interface, while all actual signal encoding/decoding (as well as compression/decompression, error correction etc.) are done by the host machine, hence the terms HAM (Host Assisted Modulation) or HSP (Host Signal Processing).

Early softmodem projects

The first softmodem-related announcements were made by Motorola, Intel and other companies, back in 1997, claiming that an ordinary sound card and some CPU power would be enough to emulate the functionality of an actual modem, although "sound card telephone adapters" and related software was never released or at least never caught on. Reasons for that might have been the lack of standarized and fully functional audio card standards by 1997 (AC'97 was not standarized yet, and most sound cards were partially functioning "Soundblaster clones" which lacked even full duplex capabilities) and the lack of CPU power on entry-level PC's.

Some of the latest softmodem chipsets e.g. the Intel Ambient 537 are even built around a standard AC'97 audio codec interface, which is pretty self-explanatory regarding the true nature of most "winmodems".

Although "Winmodem" is actually a specific brand of U.S. Robotics modem, the term has now come to mean any software-based modem (in the same way that Xerox refers to any brand of copy machine). The term linmodem is often used to denote a winmodem with support for Linux.

See also: Winprinter, Dehardwarization

External links

• A review of the differences between software-based modems and hardware-based modems (http://www.56k.com/reports/winmodem.shtml)
• A collection of resources for using Winmodems under Linux (http://www.linmodems.org)
• Lucent / Agere Winmodem driver software for Linux (http://www.heby.de/ltmodem)