Modems come in two varieties, direct connect and acoustically coupled.
The direct-connect modem hooks between the phone line and your phone, or between your phone and the handset. Its whine transmits better over static-ridden lines than do acoustic couplers, but it’s normally a little more expensive, and hard to install if your phone lacks modular plugs, the tiny plastic ones that unsnap.
Using an acoustic coupler, you cradle your handset in rubber “earmuffs.” A small speaker whines into the phone transmitter; a little microphone picks up the sound from the handset’s receiver. Acoustic couplers don’t need phones with modular plugs, obviously—a boon to traveling executives—but they might not work if the handset is oddly shaped, as it is with some of the new-style phones. Also, loud noises in the room can confuse them.
A direct-connect modem, for that reason and others, would probably be better for your regular office. Also, consider a full-duplex modem in most cases.
No, it isn’t a modem for two-family houses. “Full duplex” is just jargon for computers jabbering back and forth, both ways, at once. Like two people on the phone. A half-duplex modem would allow just one-way communications without switching; it’s somewhat comparable to a radio with an unwieldy send-receive control. There are times, however, when half duplex would be best. Normal phone lines, voice grade ones in telephone company language, can’t handle computers jabbering at too high a speed, and half duplex may work better than full.
Like most modems for personal computers in the early 1980s, Fuller’s gizmo transmitted information at 300 baud[baud]—equivalent to 300 bits a second, 30 characters per second, or 360 words per minute at 5 letters a word. When telecommuting, however, you may be better off with a modem going 1,200 baud. After all, it can zip material over the phone lines at four times the speed, and that means you’re tying up your modem less on long documents. You might not be tying up yourself if you run an operating system like Concurrent CP/M, which lets your computer handle electronic mail while you’re using it for other purposes; but a 1,200-baud modem is still a good investment if you can afford it. You may well be able to. Soon 1,200-baud modems with auto-answer features will commonly sell for well under $300.
Sent through a modem, the data bits are those conveying the information itself. And the start bits and stop bits keep track of the beginnings and ends of your micros’ characters. The most common setting is a word length of 8 data bits and 1 stop bit.
Parity bits may help the computers check for errors caused by static and other electronic noise. Parity is said to be “even,” “odd,” or “none.” This error-checking method has its drawbacks. It may fail if the mistakes cancel each other out—and it’s slow since it checks every character. Some communications programs (the ones allowing computers to talk) lack this feature. The most common parity setting is “none”—when you tell your software not to do parity checks.
A few other wrinkles in such programs are:
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