For decades, if you wished to have two computers communicate over any length of distance, you often only had one option, a analog telephone-based modem. The modem allowed for communication over telephone lines, utilizing a technology that was over a century old by the time it became accessible in the 1980s. Over time speeds became faster from 300 baud to 1200, 2400, 4800, 9600, 14.4K, 28.8K, 33.6K and finally 56K(ish). However those speeds were simply not enough to keep up with the ever growing demands of internet bandwidth and traditional modems lost out to cable modems and DSL by the early 2000s. Now with broadband available for just about anything and plain old telephone system (POTS) landlines almost completely replaced by VoIP services, can you really still use a modem today? This blog post will demonstrate how you can.
Types of Modems
The earliest modems available for general use were the acoustic couplers, an external device which connected to a computer. The acoustic coupler consisted of a base with a pair of cups into which you could place a telephone receiver. To use these devices one user would have to pick up the phone, dial a number and then put the receiver on the cups. On the other end of the line the other user would have to answer the call by picking up his receiver and placing it on his acoustic coupler. Thereafter the software would control the coupler hardware, which was capable of sending and receiving audio tones over the line representing data communication. Prior to the 1980s telephone receivers were generally of a standardized shape and were leased from the telephone company. They were often hardwired, making it difficult to access the line directly, hence why acoustic couplers were popular for early modem usage.
The TRS-80 Model 100 had an acoustic coupler which was just a pair of telephone cups connected via a cable to the computer. The hardware to drive the tones needed for communication was mostly inside the computer. The cups were not connected to each other except via a wire, this allowed for maximum flexibility for travel anywhere in the world. Telephone receivers were not quite so uniform everywhere and were evolving at a far more rapid pace during the 1980s than in previous decades.
Eventually the RJ-11 connector became commonplace and hardwired jacks became a thing of the past, allowing modems to be developed with "smart" capabilities, which at the most basic level included the ability to dial a number and answer a call without the user needing to lift a receiver or punch numbers into the phone. Thereafter modems could be classified into two types, internal and external.
Internal modems plugged into an expansion slot on a computer, which made them convenient to use if you owned a computer with a spare expansion slot. The Apple II and IBM PC had internal modems and systems like the Commodore VIC-20 and C64 plugged modems into the User Port. Internal modems are specific to a particular type of computer, you could not use an Apple II expansion-slot modem in an IBM PC and vice versa.
External modems were also popular. These boxes sat outside the computer and usually connected via a serial port. They need their own power supply but usually have LEDs to communicate status more readily than an internal modem. External modems also have the advantage in that they are not tied to a particular computer, any computer with RS-232 compatible serial should be able to use an external modem.
Modems and Gaming
Many games supported a modem for multiplayer gaming. Modems were usually not the only way people could play multiplayer games without sharing a single machine and screen, there were null modem, a.k.a. direct serial connections usually available. (MIDI Maze on the Atari ST famously used the system's MIDI ports to connect up to 16 players.) The null modem would connect the serial ports of two machines together but cross-wire the receive and transmit lines on the connection in the cable or with an adapter. The direct link had the advantage of being more reliable and with lower latency but required physical proximity (50 feet maximum) or special repeaters between the two computers.
For games from the mid-1990s onward IPX networks were often supported for multiplayer PC gaming. IPX networks can run over Ethernet, which is far faster than a serial connection. Moreover IPX can support more than two player games unlike modem or null modem connections. IPX was generally limited to local area networks, so again physical proximity was a requirement although the distances were less stringent than null modem connections. There were gaming services like Kali and Kahn which extended IPX network play to the internet. Today there is the Classic Gaming Arena which handles these connections for the modern age. However until the Internet became embraced long distance multiplayer PC gaming was handled through modems.
Battle Chess
Battle Chess is one of the earliest PC games to support a modem that can still be played today. Other early games which were modem-only multiplayer were Modem Wars and The American Challenge: A Sailing Simulation (except on PC). Unlike most later games they do not support direct serial (null-modem) connections.
It may seem absurd to play chess over a modem, you could easily pick up the telephone and relay your moves by talking to your opponent on the other end of the line. Depending on the cost of long distance, it was not a cheap game if you played for long enough because the modem's connection was continuous. Playing by mail was a far cheaper way to play long distance and if you had the licenses to operate a ham radio, you could play anyone anywhere in the world without extra cost and without the delay imposed by mail. Of course if you were one of the lucky few who had access to email, that was a cheap way to play.
There are some reasons why you might want to play over a modem. You might have want to play someone local, where long distance charges did not apply. You could also play someone who does not speak the same language or is not familiar with chess notation. You may not want to reveal your voice to a stranger. The program always moves the pieces correctly and instantly. You get to watch the funny animations if you play in the 3D mode. And if one player does not have a chess board or is missing pieces, you have software to use. Fortunately the game only requires a 300 baud modem, so anyone with a modem can play it.
In order to play Battle Chess via a modem, each player must set their opponent to the modem. Player 1 sets Blue to Modem and Player 2 sets Red to Modem. Each player must then enter a modem command, with a mouse or joystick being used a box appears when you type in any letter or number. One player types in ATS0=1, which puts the modem into auto-answer mode. The other player types in ATDT [###-###-####] which instructs the modem to dial the number entered. If a connection is established then the game will transmit and receive moves thereafter. Each player on the end of the connection can be a player or a computer, so two computers can have a game over a modem. Most versions of Battle Chess support modem play, so you should be able to have a game with one player on a PC and another on an Amiga or Macintosh.
To Landline or Not to Landline
Landline telephone service is still around today in the United States, but it is not the same kind of service which was available during the modem's heyday of the 80s and 90s. Even in those days the service was analog (at least at the last mile) and the phone company was a separate utility.
These days landlines are provided usually by the cable company (for households) and the telephone line goes into the cable modem. Alternatively VoIP services are also popular, especially for businesses. These services were originally designed for voice but have been adapted to allow acceptable facsimile transmission but as for modem data, they may not be ideal and speeds may be limited. The use of a landline signal continues to decline. My cable modem does not even have a telephone jack, I would have to use an Analog Telephone Adapter to connect an analog modem to it and pay a subscription fee in all probability.
Back in 2014 I was able to use the IBM PCjr. modem and a Tandy modem to connect to BBSs when I still had a landline. The quality of the connection was OK at 300 baud. Faster connections above 1200 baud with another PC and modem were too error prone but more modern modems have error correction built in which should assist in allowing for reliable transfer. Most BBSs these days have discontinued their ability to accept direct dial connections, now you generally access them through their IP address. There are a few still available.
Hardware and Software
I wanted to relive the experience using a modem, so I decided on a test. On one end of the line I would have a Tandy 1000 TX and on the other end a modern PC, an HP Omen I bought in 2021. I used external modems on both systems, a US Robotics 56K Serial Faxmodem (Model 5686G) and a Dell Conexant 56K USB Modem (Model RD02-D400.) For a terminal emulator I used ProComm 2.4.3 for DOS and ExtraPuTTY for Windows.
Modems were not made to connect directly to each other, they were made to connect to a Public Switched Telephone Network (PTSN). This hardware would provide enough power to supply the basic functions of a telephone as well as voltages to simulate ring tones and such. Modems also depend on these voltages to detect that a phone line is connected. Cable modems and analog telephone adapters also supply these voltages.
In order to get around a lack of a landline, one can use a telephone line simulator. These typically come in a box with two telephone jacks which can simulate a PSTN. While you can often find modems for really cheap or even free at the local electronics recycler, telephone line simulators are a bit more expensive. I have seen them go for around $125 but if you hunt around hard enough you might be able to find people practically giving them away.
I used a Ring-It! Phoneline Simulator from Digital Products Company. This device requires its own power supply. There are two phone jack inputs, a single digit LED display, a button for the mode and a button to ring. There are five modes which can be switched on the front panel, I found that Automatic Ring Mode (A.) worked best. The display will show the numbers as they are being dialed. It does not matter which modem is connected to which line, at least with this mode. It requires a 14v AC power supply (polarity is not relevant to AC) with a Type-A barrel jack.
When I connected both the Tandy TX and HP Omen modems together through the phone line simulator, I started up Battle Chess on both systems, set the other player to Modem and typed in the appropriate commands. I used 555-1234 as the number but anything seven digits or more should do. To my surprise it worked right away after hearing the familiar handshaking tones not too unlike this. Moves were sent and appeared on the other screen almost instantly.
The Wider World
The experiment referenced in the previous section is interesting as an experiment or a proof of concept, but the point of a modem is to connect to people remotely, not as an unnecessarily complex substitute for a null-modem cable. You want a modem to "call" another computer, but if you do not have direct access to what passes for the landline network these days, you are out of luck. Or are you?
When the Internet became popular, people would subscribe to a service which provided access to the Internet and allowed them to dial into a server which would allow their modem to send and receive data from that server. The server would be responsible for retrieving the requested data from the site and sending it back to the modem. Today we have software which can simulate a dial-up ISP. Slow internet loses its charm quickly and almost all of the popular vintage non-PC systems have affordable Ethernet options these days.
Getting your modem to connect through an emulated ISP is a first step. The ultimate test is of course to connect directly to another individual's computer remotely. When I get around to a Part 2 of this series, I hope to be able to describe a software solution for this problem.
