In the earliest buildups, each line terminated on a single machine at Compu Serve's host, so different numbers had to be used to reach different computers.
Later, the central multiplexers in Columbus were replaced with PDP-8 minicomputers, and the PDP-8s were connected to a DEC PDP-15 minicomputer that acted as switches so a phone number was not tied to a particular destination host.
In 1981, The Times explained Compu Serve's technology in one sentence: Compu Serve was also a world leader in other commercial services.
Barry Berkov was recruited from Xerox to head product development and marketing.
In 1977, Compu Serve's board changed the company's name to Compu Serve Incorporated. The original 1969 dial-up technology was fairly simple—the local phone number in Cleveland, for example, was a line connected to a time-division multiplexer that connected via a leased line to a matched multiplexer in Columbus that was connected to a time-sharing host system.
At its peak in the early 1990s, CIS was known for its online chat system, message forums covering a variety of topics, extensive software libraries for most computer platforms, and a series of popular online games, notably Mega Wars III and Island of Kesmai.
It also was known for its introduction of the GIF format for pictures, and as a GIF exchange mechanism.
Compu Serve developed extensive screening and reporting tools that were used by many investment banks on Wall Street.
In 1978, Radio Shack marketed the residential information service Micro NET, in which home users accessed the computers during evening hours, when the Compu Serve computers were otherwise idle.
It was spun off as a separate company in 1975, trading on the NASDAQ under the symbol CMPU.
Concurrently, the company recruited executives who shifted the focus from offering time-sharing services, in which customers wrote their own applications, to one that was focused on packaged applications.
The first of these new executives was Robert Tillson, who left Service Bureau Corporation (then a subsidiary of Control Data Corporation, but originally formed as a division of IBM) to become Compu Serve's Executive Vice President of Marketing.
He then recruited Charles Mc Call (who followed Jeff Wilkins as CEO, and later became CEO of medical information firm HBO & Co.), Maury Cox (who became CEO after the departure of Mc Call), and Robert Massey (who followed Cox as CEO).
CIS finally introduced monthly pricing in late 1997, but by that time the number of users leaving all online services for dialup Internet service providers was reaching a crescendo.