The ins and outs of your PC's communications


August 29, 1994|By MICHAEL J. HIMOWITZ

With all the hype about the Internet lately, a lot of people are thinking about buying modems, or replacing older, low-speed modems with faster models.

As a result, one of the frequent questions I get is whether to buy an internal or external modem. On the whole, I come down on the side of an external modem, but there are reasons to consider an internal unit.

First things first. Internal and external modems do exactly the same thing. They allow your computer to communicate over phone lines with other computers. From a communications standpoint, there's no theoretical advantage to either. The question is how they attach themselves to your PC, and whether one type is more convenient than the other.

An external modem is in a box that sits outside your computer, but modems today don't take up much real estate. The Practical Peripherals modem I use, for example, is about the size of a paperback book.

External modems connect to your computer's serial port with a cable. The serial port is actually an outlet on your machine's Input-Output (I/O) card, a circuit board inside your computer that handles external communications. Most I/O cards usually contain a parallel port for your printer, in addition to one or more serial ports. Most computers today have two serial ports. The first is usually used by a mouse, the second for a modem or some other device.

Newer computers often include disk drive controllers on the same circuit board, which can save space and money.

An internal modem is a circuit card that fits into one of the expansion slots inside your computer. It contains its own serial port circuitry, as well as the modem's electronics. At the back of the card, facing the outside world, you'll find one or more jacks that connect to your wall line and phone with standard telephone cord.

The main advantage of an external modem is that it lets you see what's going on with your communications session. Getting two computers to talk is still half science and half voodoo. You'll need whatever edge you can find.

Every external modem has a row of little lights that shows you how things are progressing. The light labeled CD (Carrier Detect) tells you whether you are, in fact, connected to another computer. Lights labled RX and TX blink on and off when you're receiving or transmitting data, respectively. A light labeled AA will tell you if your modem is set to auto-answer the phone, a feature you'll want to turn on if another computer is calling yours, but one you'll want to turn off when you're not expecting a computer call.

Was it a glitch?

Some modems have more lights than others, but all of them will display the basic information you need, particularly when something goes wrong. Let's say you dial up an information service or another computer and make connection, but nothing happens. Are you really connected, or did some glitch bounce you off the line? The CD light will tell you.

If you have indeed made the basic connection, are your machine and the other computer exchanging data? If you type something and neither the RX nor the TX light blinks, you're not really communicating. Likewise, if you're logged onto an on-line service, request a piece of information and get no immediate response on your screen, the RX and TX lights will tell you whether the other system is just busy sending data or whether it has just left you hanging there (America OnLine does this a lot).

With an internal modem, you never really know where you stand. If you're having a problem contacting another computer, you can't even tell whether you're making the initial connection, let alone whether you're receiving and transmitting. Some communications programs, particularly those operating under Microsoft Windows, can help with this problem by displaying a graphic of a modem, complete with CD, RX, TX, AA and other lights that blink at the proper times. But with most software, you're in the dark.

The gods don't smile

Another advantage of an external modem becomes obvious when things get hung up beyond repair and the modem stops responding to commands. This will happen from time to time. As I mentioned earlier, communication is half voodoo and the gods do not always smile.

To reset an external modem that's completely hung up, all you have to do is turn it off and turn it on again (a time honored fix). With an internal modem, which gets its power from the computer, you have to turn the computer on and off, which is a pain in the neck if you're in the middle of a project, not to mention being of questionable value to the computer.

Finally, an internal modem takes up an expansion slot on your motherboard. If you have a large board with a bunch of open slots, this doesn't matter. But if you have a compact machine with only two or three open slots, the modem takes up space that could be occupied by sound boards or controllers for CD-ROMS, scanners or other devices. An external modem uses the circuitry in your existing I/O card.

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