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[ The PC Guide | The PC Buyer's Guide | Designing and Specifying PC Systems and Components | Detailed Considerations and Tips for Specifying Particular Components ]


Description: A modem is a device that converts data into a different energy form for transmission over some sort of connection, and then converts that energy back into data again on the other end. When the term "modem" is used by itself it usually refers to a regular, analog modem that functions on a regular phone line. The term "modem" is a contraction for "MOdulator-DEModulator"; modulation is the process of converting data into sound.

Regular analog modems are still used by the vast majority of PC users for connecting to the Internet, sending faxes by PC and similar tasks. However, there are other types of modems as well: cable modems for Internet access over television cable, DSL modems for DSL Internet access and so on. These are usually not sold with new PCs and I will not be covering them here, just regular modems.

Role and Subsystems: The modem is part of the communications subsystem. It connects to the system in one of several different ways, depending on the exact type. Internal modems plug into a bus slot in the motherboard; external modems connect through a serial port, which is also connected to the motherboard. These are fairly standardized interfaces, and so have little impact on motherboard specification issues.

Related Components: The motherboard, but only rather loosely.

Key Compatibility Selection Criteria: Modems are fairly mundane components today (see the discussion under performance criteria for more), connecting to the system in one of a handful of standard ways. You will need to make only one or two key decisions in deciding specifically what you want to get:

  • External vs. Internal: Most modems are internal devices that plug into a system bus slot, but external modems are available as well. An external modem is a small box that connects to the PC through a serial I/O port. Some people prefer external modems for a few reasons: they are easier to install into an existing system (assuming you have a free serial port), they come with status indicator lights, and you can reset them without having to reset the entire PC. Furthermore, with an external, you always know you have a full hardware modem, not a host-based modem (see the performance discussion for more). The drawbacks of external modems include increased cost and space requirements. For new PCs internal modems are far more common.

Note: Do not use an external modem unless your system has 16550 UARTs in its serial ports. Almost all new machines do, but if yours does not you will not be able to achieve high connection speeds. Serial ports are usually integrated on the motherboard and therefore not replaceable.

  • Bus Type: Assuming that you are getting an internal modem, you have a choice of whether to get an ISA bus modem or a PCI bus unit. This decision usually comes down to what slots your motherboard has available, and whether you are trying to reuse a device from an older system. Until a few years ago all modems were ISA, so there are millions of them still out there, and you may want to use one in a new system to save money. New systems in the future will be harder than ever to find with ISA slots though, so for a new modem PCI is probably best, assuming the motherboard has room for it.
  • Operating System Support: If you want to use an operating system other than Windows, you may have a problem with host-based "Winmodems". Be sure to get a real hardware modem for DOS or Linux use. See below for more discussion on the differences between the two.

Performance and Capacity Selection Criteria: It's somewhat ironic, given the history of the modem, but there really aren't many performance issues involved in choosing a modem any more. During the 1980s and 1990s, analog modem standards were changing rapidly and you had to be very careful about what sort of modem you purchased; you had to decide if you wanted to spend more to get a faster unit or less for a slower one. There was also a period when there were two different competing 56K modem standards.

Today, the market has become standardized, and it has been some time since the last advance in analog modem performance. This means almost all analog modems sold today are 56K V.90 modems. There really aren't any other kinds sold any more.

The only real performance decision that remains is this one: do you want to get a real modem, or a host-based modem? Real modems include all processing capabilities in hardware on the modem itself. Host-based modems, also frequently called software modems or Winmodems, save a few bucks in cost by replacing some of the processing capabilities with software drivers. This saves money for the manufacturer, but means that whenever your modem is running, your system is partially slowed down by the CPU doing modem work. The hit can be significant.

Needless to say, if you really care about performance you do not want a modem of this sort. Then again, if you don't do much while your modem is operating, and your CPU is fast enough to handle the load, this may be an acceptable way to economize. If you do a lot of gaming over the Internet, you will most definitely want to avoid Winmodems, because you won't want to waste precious CPU cycles on modem tasks.

Quality Selection Criteria: The fact that analog modem technology has stagnated means that current designs are relatively stable, and quality is generally stable as well. There isn't a lot by which to differentiate units on the basis of quality. Quality is important, because poor units can make your life miserable by refusing to connect, hanging up or connecting at slow speeds. Assessing quality comes down to researching specific companies and sticking to known name brands when possible (which usually are close to the cost of generics anyway).

Important Features: Pretty much all modems support regular data connections and also faxing (both send and receive). Beyond this, some modems include additional telephony features. For example, some will let your PC act as an answering machine, or do voice mail. If you think you'll make use of such features you may want to look for them. I must say that I think it's a waste to leave your PC on all the time to answer phone calls when you are away, given that a good answering machine costs what, $50? :^) But there are some for whom this is valuable.

"Magic Numbers" To Watch For: As I mentioned, virtually all modems today are "56K" modems. Most PC users already realize that this means the modem is theoretically capable of 56,000 bits per second throughput, but that they are not likely to actually get a number that high. About 50,000 seems to be the highest most people get, and many get much less. You must have good phone lines to get connections above 33,600, and some get only 28,800 or less, even with good modems. That's especially true in rural areas.

Performance Impact: None for regular uses, but for Internet use it is pivotal. Despite all the marketing hoo-hah about new PCs or fast CPUs "speeding up the Internet", the modem is still the bottleneck for most applications involving the Web. Upgrading to a faster modem (if you are still using a slow one) will actually speed up the Internet--going to a faster type of connection and leaving analog modems behind is even better.

Retail, OEM and Gray Market Issues: Modems are often sold as OEM items. This is usually not a problem if you stick to known brands. I don't consider buying a retail package to be as important for modems as other components, simply because of their relative uniformity and simplicity today.

Importance of Manufacturer: Not terribly essential, but do yourself a favor and don't get the cheapest modem you can find. Stick to one of the better-known brands if it's not much more to do so.

Typical Component Lifetime: Modems generally last for many years and I don't expect analog modems to change much in the near future. However, recognize that as higher-speed Internet connectivity becomes more available, more and more people are leaving their analog modems behind...

Warranty Issues: Nothing special.

Driver Support Issues: For hardware modems there are few issues, but Winmodems can cause considerable problems because for this type, the driver is actually part of the modem. If you want to run Linux or another "unusual" operating system these devices may not function at all.

Special Specification Considerations: None.

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