Dial ‘M’ for Modem . . . and Muddle
If your computer isn’t equipped with a modem, you’re missing a lot. A modem is the device that translates a computer’s digital signals into sounds that can be transmitted over telephone lines.
Shopping for a modem can be quite confusing. A variety of relatively obscure “standards” can boggle a prospective buyer.
You’ll need a modem if you want to use the phone to communicate with another computer. On-line information services such as America Online, CompuServe, Genie or Prodigy provide a wealth of information, including news, weather, sports and the ability to send electronic mail. Modems also let you connect to computer bulletin boards where you can “download” software for free and pay only if you decide to keep it. And, for an increasing number of people, modems serve as the link between their home and office computers.
Of the hundreds of modem makers, the leading vendors include Hayes, Intel, Practical Peripherals and U.S. Robotics. You should also check around for bargain brands which, in many cases, are also very reliable.
Speed is a major consideration. Modems are rated in bits per second (bps). Today, anything less than 2,400 bps is obsolete, and an increasing number of buyers are opting for modems that run at 9,600 or even 14,400 bps. A speed of 2,400 bps translates to roughly 300 characters per second or 3,000 words per minute.
If you plan to use a modem primarily to read information from on-line services, then 2,400 is fast enough. However, if you plan to transfer data or programs between computers, you can benefit from a faster modem. Many people, for example, use their modems to connect to bulletin boards where they can download software. At 2,400 bps it would take about 28 minutes to download a 500-kilobyte program, instead of seven minutes at 9,600 bps. You can find 2,400 bps modems for under $100; 9,600 and 14,400 bps modems generally cost $350 or more.
If you’re buying a modem for an IBM-compatible machine, you’ll have to choose between internal and external. An internal modem is a circuit board that plugs into one of the PC’s expansion slots inside the case. An external modem sits on your desk and is connected by a cable to the computer’s serial port, a socket at the back of the case.
Internal modems are generally cheaper and they don’t take up any desk space or require any cables. I prefer external modems for a number of reasons. You don’t have to take the PC apart. They don’t take up an expansion slot, and you can move them from machine to machine. What’s more, most external modems have lights or displays that provide visual feedback regarding their status. U.S. Robotics, (800) 342-5877, and Macronix, (800) 468-4629, make battery-operated, pocket-size modems that work with both portable and desktop machines. Whatever modem you get, be sure it has a speaker so you can hear the dial tone and connection. Without that feedback, you may not be sure whether you’ve gotten through.
A growing number of data modems are also able to transmit and receive fax messages. Most fax/data modems come with the required facsimile software. The extra cost for fax capability is sometimes quite low, so it’s worth considering.
Performance can be affected by the modem’s ability to compress data. By compressing data, the modem automatically reduces the size of files so that there are fewer bytes to transfer. The modem on the other end then decompresses the file so that it’s identical to the original.
There are a number of compression methods available, but the current international standard is called V.42 bis. Bis is French for encore or second try . That method, under ideal conditions, is able to increase data transmission by a factor of four, so that a 9,600 bps modem, in theory, could transmit files at 38,400 bps. But both sender and receiver must have a V.42 bis modem for that to occur. Many bulletin board services and corporate computers support V.42 bis, but most on-line services do not, although you can still communicate with them.
Don’t confuse V.42 bis with V.42. V.42 (without the bis) refers to the modem’s ability to detect and correct errors. Two modems with the same error correction protocol are able to verify whether the data received is identical to what was sent. You don’t need an error-correcting modem for reliable data transfer. Just about all communication programs handle error detection and correction via software.
Another set of numbers indicates compatibility with international standards. For 2,400 bps, look for V.22 bis. The current standard for 4,800 and 9,600 bps is called V.32 bis, which supports up to 14,400 bps.
Don’t get too bogged down with these confusing standards and numbers. While knowing the difference between various modems can help you better understand a sales pitch, just about any modem will be fine for most users.
