If you do decide to buy a new 56-kilobit/sec modem, shop carefully -

If your Internet provider doesn't support 56-kilobit/sec modem downloads, you probably
wonder why I'm writing about this topic again.

I believe new technology is always important for power users to know about, even when
it doesn't work as advertised. In this case the fast new modems actually do work, they
just don't squeeze data through the pipe as fast as they claim.

But then who ever had a 33.6-kilobit/sec modem that could reach that speed in the real
world? I certainly didn't.

I've been testing a lot of the new modems for longer or shorter times and over various
phone connections. My conclusion is that if you need a new modem anyway, you should make
it a 56-kilobit/sec one, if only because they all default to 33.6 anyway. You won't have
to pay a big price premium.

When it comes to choosing a particular brand, that isn't as easy. Make certain the
modem you choose can be upgraded easily once the standards wars settle down.

If you already have a 33.6- or 28.8-kilobit/sec modem that you like, the situation gets
murkier.

One thing I can guarantee is that you will never see 56 kilobits/sec out of any of
these modems, even if that speed didn't violate Federal Communications Commission rules
[GCN, Sept. 8, Page 58]. But you probably will see an incremental performance gain along
the lines of what we got in the move from 28.8- to 33.6-kilobit/sec modems a few years
ago.

The same buying rules still apply. If the price is right, go ahead and buy. You'll see
a speed improvement whenever you connect to a remote site that has modem equipment
following the same standard as yours.

The best uncompressed speed I saw, tested with precompressed files, was about 40
kilobits/sec with a K56flex modem from Zoom Telephonics Inc. of Boston. Results were
almost as good with modems from Hayes Microcomputer Products Inc. of Atlanta, Practical
Peripherals Inc. of Norcross, Ga., and Motorola Inc., all containing the same Rockwell
International Corp. chip set.

In real-world testing, it was difficult to tell which was fastest. Line conditions
could change from second to second, and some modems did better than others on dirty lines.

The average speed of modems containing the Texas Instruments Inc. x2 chip set was a bit
slower, except for U.S. Robotics Access Corp.'s Courier V.Everything modem, which was the
fastest I saw on any line. But at $275 list, it was also more expensive than K56flex
competitors that were only a few percentage points slower.

If you move a lot of .zip files that aren't precompressed, your modem tries to compress
the data internally. This is where differences really show up.

My K56flex test modems achieved real-world compression throughput of about 85
kilobits/sec, and x2 modems did about 10 to 20 kilobits/sec better.

A bottleneck comes into play when you download large files--why else would you need a
fast modem anyway? Modems have internal caches that speed throughput for small files of,
say, 20K or so. Larger files have to be decompressed on the fly.

Here's where your computer's serial port may fall behind the modem and slow it down
artificially by creating a data flow bottleneck from modem to PC. That was why I tested
only external modems using a high-speed LavaPort serial port board from Lava Computer
Manufacturing Inc. of Rexdale, Ont.

This fast serial port did make a difference in real-world throughput, although it was a
relatively small difference. But the LavaPort is worth its $60 price tag for most power
users. It can support up to 460.5 kilobits/sec if you tweak your software.

Microsoft Windows 3.x environments max out at 115.2 kilobits/sec, but the LavaPort
includes software to work around this limitation.

Note that just because a file doesn't have a .zip extension doesn't mean it isn't
compressed. Some .exe files, including those you download from the Internet, expand a lot
when you try to install them.

In fact, if you mostly download large files from the World Wide Web, you won't see any
modem compression, because virtually all downloadable files are precompressed one way or
another, either as .zip files, compressed audio-video or self-extracting files.

Bottom line: Don't buy a 56-kilobit/sec modem you can't easily upgrade. There is no
standard yet. And find out whether your remote provider or server uses x2 or 56Kflex
modems. If it doesn't have either, you won't see any performance gains no matter what.

Don't expect 56-kilobit/sec raw throughput or anything better than about 90-kilobit/sec
average maximum throughput including modem decompression.

Buy one of the new modems if you need one anyhow, and if the price difference between a
33.6-kilobit/sec model and the new one is minor. 56Kflex and x2 are backward-compatible
with slower standards.

On the K56flex side of the market, look first at Zoom Telephonics' Zoom/FaxModem 56K or
Motorola's VoiceSurfr 56K. On the x2 side, consider U.S. Robotics' V.Everything external
modem if price is no object. Its main competitor is Practical Peripherals' PM 56K Mini
Tower, which is noticeably slower and only about $30 cheaper.

All four of these should be easy to upgrade via flash erasable programmable read-only
memory when the time comes.

Buy from other vendors following either standard if their prices are considerably lower
and the modems can be upgraded easily. We may see performance improvements as the bundled
software matures.

Consider any special features you need such as callback, remote configuration or
automatic carrier redial. These features might matter more to you than raw speed.

John McCormick, a free-lance writer and computer consultant, has been working with
computers since the early 1960s. E-mail him at powerusr@penn.com.