Beware Soft Modems
When you buy your next modem, you could innocently buy a software-based modem, not realizing the limitations of what you're buying.
Why soft modems are different
Software-based modems use fewer chips compared to traditional modems. The work normally done by the missing chips is transferred to software running on the host computer's main processor (the Pentium, PowerPC, etc.).
Modems consist of two major components:
A traditional modem implements both features in hardware, as chips inside the modem.
A controllerless modem, such as the U.S. Robotics (now 3Com) Winmodem, still has a hardware datapump, but implements the controller function as software.
An HSP modem dispenses with both the controller and the datapump, and uses software to provide both functions. Short for host signal processor, HSP modems transfer the work normally done by the missing chips to software running on the host computer's main processor (the 486, Pentium, PowerPC, etc.)
How do you know if it's a software modem?
There are a number of clues that your modem is software based:
There are a number of flaws in the soft modem concept. In all cases, your host computer has to do more work to make up for the modem's lack of hardware. One RPI modem user reported slow transfer rates and dropped connections until he upgraded his PC from eight to sixteen megabytes of RAM (which improves performance in Windows). IBM's minimum requirements for the 56K Internet Kit modem is a 486, but some features require a 90 MHz Pentium, and DSVD features require a 133 MHz Pentium.
Note that U.S. Robotics Winmodems and other controllless modems have an on-board DSP that takes care of basic modulation and de-modulation tasks, so the load on the host computer is minimal. A number of USR Winmodem users have written in to say that they have been very pleased with the performance of their modem, and hadn't noticed any slowdown on their computer.
The other big disadvantage of software-based modems is that the software needed to make them work is operating-system dependent. Apple's GeoPort Telecom Adapters require the Mac operating system, so they won't work with MKlinux or Be OS. Other soft modems are generally Windows-only, so they can't be used with Linux, Solaris, OpenStep, or OS/2 unless someone writes special drivers. In contrast, any external Hayes-compatible modem with a full chip set can be used with any operating system on any computer with a serial port.
Even if you don't plan to run Linux on your PC, you may want to play modem-to-modem games like Doom that run in DOS. DOS games generally won't work with Winmodems, unless DOS drivers are provided. Major exception: Quake will still work, because Quake runs in a DOS shell under Window, and uses the Windows network drivers.
Winmodem configuration can be messy, because Winmodems use a range of memory addresses instead of a fixed memory address. Winmodems require a DLL file that loads into memory at startup, using some of Windows' resources.
If software-based have these problems, why do they continue to sell? In part, the answer is cost. By omitting a few chips, manufacturers can sell Winmodems for twenty to fifty dollars less than traditional modems. In an era of thousand dollar PCs and handheld consumer devices, cost is an enormous issue.
Soft modems are also popular for features like DSVD (digital simultaneous voice and data) and answering machine features, which are easier to implement with a soft modem.
Soft modems have some real benefits in small devices, such as laptop and hand held computers. They weigh less than traditional modems and take up less space. They also consume less electricity, which makes them ideal for battery-powered devices.
The upgradeability of soft modems is mixed. RPI modems aren't upgradeable to anything beyond a 14.4. After years of delays, Apple finally released a free 33.6 software upgrade for the 14.4 Power Mac GeoPorts, but not the Quadra AV GeoPorts. Apple has no plans for a 56K upgrade. U.S. Robotics had a free software-based 56K upgrade for some Sportster 33.6 Winmodems, but not others..
Upgradeability is one area where purely software-based HSP modems have an advantage over traditional modems and controllerless modems. Because almost every aspect of the modem is in software, the modem is highly upgradeable.
For another perspective on the pros and cons of soft modem use, see Tom Herbert's "Integrating a Soft Modem."
In general, I recommend avoiding HSP modems. Get a good old-fashioned modem with all of its chips intact. Nothing else offers the same level of reliability, compatibility, and performance. The small savings of buying a Winmodem doesn't compensate for the load it shifts to your expensive new Pentium. And if you're an online gamer, you definitely want to avoid Winmodems.
Winmodems have their advantages. If you plan to only use Windows, and if gaming isn't your thing, a Winmodem can save you money, and it may offer more telephony features than a similarly-priced modem.
- Les Jones
Lee Schneider wrote in with some notes on his Multiwave modem, many of which apply to Winmodems in general:
1.These modems require a faster processor to connect at high speeds. A P100 is marginal for a 28.8 to 33.6 connection. A P133 is better and anything faster works fine. A P75 will generally not connect at 28.8. (Forget a 486)
Embedded Systems Programming - "Integrating a Soft
Windows Sources - U.S. Robotics Sportster Winmodem
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