11 Aug 1996

Types of Modems

Many vendors give away modems with every new computer system. You get what you pay for. A modem selling for $50 (retail) will support only 2400 baud (2400 bits per second transmission rate) for data. The same modem will generally transmit FAX, and because images contain long sequences of blank white paper followed by sequences of black ink, they compress easily. When a modem is transmitting data at 2400 baud, its effective rate of FAX transmission (before compression) may be equal to 9600 baud. The vendors may call this a 2400/9600 baud modem and then try to confuse the buyer to remember the 9600 part. Such practice borders on fraud. It is still a 2400 baud modem, and in current use it is a "piece of junk." It should not be long before 2400 baud modems are given away free inside every box of Fruit Loops (introducing the era of "cereal communications").

There are five types of modems that you might encounter.

A V.32 modem supports 9600 baud data communications. It is unlikely that any of these are still for sale, but many are still in use at companies. IBM got into a lot of trouble at the Olympics in Atlanta when foreign news organizations came with modems that could only do 9600 baud to a system that expected a higher rate of data transfer.
A V.32 bis modem supports 14,400 baud data communications. This is a good solid middle of the road standard unit. Data compression and error recovery typically use V.42 bis protocol.
A V.34 is the latest standard. It supports communications at 28,800 baud. Vendors spent the last few months developing and testing hardware. Now volume production has begun and these units are beginning to appear in stores. Expect pricing around $250.
Some modems run a bit faster than 28,800. There is no standard here, so you have to buy the same type of modem at both ends of the connection. Otherwise, they will fall back to the V.34 standard.
Though not strictly a modem, an ISDN adapter can be used with ISDN digital phone service if it is offered by the local phone company. This can provide support speeds of 64000 bits per second. More will be said about this option later on.

A V.34 modem will cost from $100 to $140. An "internal mode" comes on a card that plugs into the ISA bus of the computer. Internal modems are less expensive, because they get their power from the CPU. They also ensure that the COM port hardware is adequate for the supported speeds. External modems cost a bit more but require no slot.

An external modem also provides a front panel with LEDs that represent the status of various modem lights. In the old days, when modems were relatively simple devices, thes status lights were important for problem determination. However, the new generation of smart modems will ususally generate an error message when anything goes wrong. The newer operating systems, such as Windows 95 or Windows NT, will detect or can be configured for a particular modem model. The system then becomes responsible for programming the modem options and handling the error codes. These systems can also display the status of the modem leads in a Window on the computer screen. Therefore, while it is true that the lights on external modems are useful in debugging, this advantage is becoming less important.

Configuring COM3 or COM4

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