At that time, most people were familiar with citizen's band radio, often abbreviated as CB radio, but multi-user chat and instant messaging were largely unknown. CompuServe CB used the CB radio paradigm to help users understand the new concept.
Like CB radio it had 40 "channels" and commands like "tune", "squelch", and "monitor". CompuServe CB quickly became the largest single product on CompuServe despite virtually no marketing. When 40 channels were not enough, additional "bands" were added, such as the "Adult" band.
In October 1983 CBSIM CB Simulator was written and released by Jerry Thomas Hunter as the first publicly accessible CB Simulator software available for privately operated computer bulletin board systems (BBSs). The program was released as "freeware" as an add-on module (or "Door") for the popular RBBS-PC. It enabled users connected on one node of a bulletin board system to "chat" with users dialed in on other nodes.
Initially, CBSIM supported a maximum of 32 concurrent nodes (connected users), and allowed dynamic creation and cataloging of "channels" by the users of the BBS on which it was installed. The source code was released to the public from the inception of the CBSIM project, and this source code quickly became the foundation for multi-node chat systems embedded in other popular BBS software products.
According to en.wikipedia