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A Brief Primer on Modems
This page is a very brief introduction to modem technology. It is written as a general one-stop answer to questions such as "what is a Winmodem, and what are the disadvantages?" It does not attempt to discuss the fundamentals of data communication; that topic will be left for a future article if there is a demand for it.
Let's begin with a naming of parts. The basic functional components of a modem are as follows:
Conceptually, all modems contain these modules. However, particularly in recent years, manufacturers have found ways to integrate functionality into fewer components, and they have also made efforts to move functionality out of expensive hardware and into software running on the host computer. As with most other fields, when price reduction becomes a priority, performance tends to suffer.
One of the first attempts to cut down on modem price was taken by Rockwell. They developed a modem referred to as "RPI" (Rockwell Protocol Interface). This modem consisted of a supervisor, supervisor ROM, datapump and DAA only. It did NOT include any supervisor scratch RAM; hence these modems were rather cheaper than regular modems. They were only available in 14400kbps speed.
The disadvantage of an RPI modem is that the supervisor doesn't have enough RAM available to it on-board the modem to be able to perform the error correction and data compression features which are standard on normal modems. Rockwell provided special driver software to make the modem appear normal inside Windows 3.x; if you were using any other operating system, though, the modem's performance was severely compromised. The Windows drivers were also quite unstable in my experience. As the prices of RAM chips started to plummet, RPI modems became less and less attractive to manufacture; they are no longer made and are quite rare.
Nasty as they are, RPI modems are preferable to the current fad of cheap controllerless modems (also referred to as Winmodems or soft-modems. Winmodem was the proprietary trade name of the first commonly available soft-modem, sold by US Robotics. In fact, the first Winmodems were literally given away, for market research purposes).
The controllerless modem was, to the best of my knowledge, first implemented in certain IBM ThinkPads, which contained an "MWave" device that was both a sound card and a modem. A controllerless modem is really just like a sound card with a phone jack on it instead of speaker and microphone jacks. It is JUST a DSP, DSP scratch RAM, and DAA. The computer needs to supervise the DSP at all times; to do this, special driver software is required.
There are now many different brands of controllerless modem, and many computer manufacturers (in fact, most computer manufacturers) bundle them as standard. When they work, they work reasonably well (driver bugs aside), but they have several serious limitations:
There are three advantages to the controllerless modem, which I will state for fairness' sake:
The ultimate recommendation I am trying to make clear here is: avoid hardware that requires strange operating-system-specific drivers, and specifically, avoid bizarre modem technologies. RPI and controllerless (Winmodems, soft-modems) are a very good example of the old adage that "you don't get something for nothing". A "real" 56K modem is frequently available for under $30 from sites like Surplus Direct; don't waste your money on a substandard piece of hardware!