SAGE’s use of telephone lines to communicate from computer to computer and computer to radar laid the groundwork for modems. The control program, the largest real-time computer program written at that time, spawned a new profession, software engineering. From MIT’s Lincoln Laboratory website:The SAGE system, by the time of its full deployment, consisted of 100s of radars, 24 direction centers, and 3 combat centers spread throughout the U.S. The direction centers were connected to 100s of airfields and surface-to-air missile sites, providing a multilayered engagement capability. These computers hosted programs that consisted of over 500,000 lines of code and executed over 25,000 instructions—by far the largest computer programs ever written at that time.

Source: Forbes January 15, 2017 17:27 UTC