The biggest codebases in history
Quincy Larson
1K12

What about the codebase for phone network digital switches?

The control program for the AT&T 5ESS digital telephone was 5 million lines of code developed by more than two thousand five hundred (2,500) developers. Pure coincidence that 5ESS had 5 million lines of code in the control program.

Now that 5 million lines of code represented the delivered product which means that a lot more software was required for testing and developer tools. Moreover, the 5 million lines of code only represented the control program. There were also modules of code for the various types of trunk lines, of which there were a wide variety given the evolution of the telephone system. Some trunk lines were in operation from at least the 1950s and perhaps some from earlier. in addition to the control program, there were different modules required for the different signalling protocols used in countries other than the United States.

Do you have any figures for the number of total lines of code required to develop and the test the 5ESS control program as well as the additional software required for all the various switch signalling protocols required for 5ESS telephone switch?