Complex sentence: When modems were slow, considerable effort was put into developing the most efficient protocols and display systems possible, and running a general-purpose protocol like TCP/IP over a 1200 bit/s modem was a painful experience.
Split into simpler sentences: When modems were slow, considerable effort was put into developing the most efficient protocols and display systems possible. Running a general-purpose protocol like TCP/IP over a 1200 bit/s modem was a painful experience.