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Semi-Automatic Ground Environment (SAGE)
In the 1950's MITRE's founders played a key role in the development of the Semi-Automatic Ground Environment (SAGE) system, the first major real-time, computer-based command and control system. Designed as a new air defense system to protect the United States from long-range bombers and other weapons, the SAGE system sent information from geographically dispersed radars over telephone lines and gathered it at a central location for processing by a newly designed, large-scale digital computer. As the system evolved, SAGE broke new ground in radar, communications, computer, information display, and computer programming technologies.
Developing a system of SAGE's size required a novel organization that could examine all facets of the problem without regard to the traditional boundaries between the military, industry and academia. In 1958, in response to this need, The MITRE Corporation was formed out of the Computer System Division of the Massachusetts Institute of Technology (MIT) Lincoln Laboratories. Much of MITRE's initial work focused on the software development of SAGE's digital computer system, radar surveillance, communications, and weapons integration. More importantly however, MITRE had the role of integrating many elements of the SAGE system—this experience established MITRE as a leader in the new discipline of systems engineering.
The SAGE system was fully deployed in 1963; the 24 SAGE Direction Centers and three SAGE Combat Centers were spread throughout the U.S. Each was linked by long-distance telephone lines to more than 100 interoperating air defense elements, requiring system integration on a scale previously unimagined. At the heart of each center was a new large-scale digital computer that had evolved from MIT's experimental Whirlwind computer of the 1950's. The largest real-time computer program of that time, it automated information flow, processed and presented data to 100 operator stations, and provided control information to the weapons systems. This processed information, including aircraft tracks and identification, was presented to operators on a cathode ray tube—one of the first uses of this device to display computer-generated data.
In spite of this complexity, remarkable for its time, SAGE exceeded virtually all the original stringent requirements, and was continuously in operation for more than 25 years. The system engineering expertise MITRE developed in the SAGE program laid the groundwork for modern command and control systems and led to a long-term collaborative partnership between the Air Force and MITRE. In addition, MITRE's SAGE work was directly applicable to another important mission—air traffic control. Through our partnership with the FAA, MITRE continues to contribute to the development of a safe, efficient and collaborative worldwide air traffic management system.
SAGE: The System in Action
SAGE: The People Behind It
"I was struck at the time and have been struck since by how much a group of really smart, dedicated people with adequate resources can do toward solving problems. You put them to work on a program, and if you don't box them with too many restrictions, you get a solution."
Robert R. Everett
"One of the outstanding things... was the esprit de corps—the spirit that pervaded the operation. Everyone had a sense of purpose—a sense of doing something important. People felt the pressure and had the desire to solve the air defense problem, although there was often disagreement as to how to achieve that end. Energy was directed more toward solving individual problems, such as making a workable high-speed memory or a useable data link, than it was toward solving the problem of the value of the finished product. It was an engineer's dream."
John F. Jacobs
SAGE: Impact on the Computers of Today
SAGE had a fundamental impact on the development of computers and the computer industry. When the program began, work on the first digital computer, MIT's Whirlwind, was in progress. Key to the success of SAGE was the development of a production version of MIT's prototype Whirlwind computer. A little known company called IBM won the contract to design and build the Whirlwind II, otherwise known as AN/FSQ-7, for the proposed new air defense system. When complete, the AN/FSQ-7 weighed 250 tons, and required a 3,000kW power supply and over 49,000 vacuum tubes. When SAGE became fully operational, it relied on 24 AN/FSQ-7s; they remained in service until the Air Force ended the SAGE program in 1983.
Looking back at the development of the computers supporting the SAGE, the origins of many key computer innovations are readily apparent. SAGE's use of telephone lines to communicate from computer to computer and computer to radar laid the groundwork for modern-day modems. Former MITRE President Bob Everett's invention of the light gun is often referred to as one of the precursor's to today's computer mouse. Whirlwind's control program, the largest real-time computer program written at that time, spawned a new profession, software development engineers and programmers.
Many other computer breakthroughs such as magnetic-core storage, modular design, interactive graphic displays, on-line common databases, and continuous and reliable operation can also be traced to the development of Whirlwind. In addition, software innovations like the ability to accommodate multiple, simultaneous users, the use of advanced data system structures, structured program modules, and global data definitions grew out of SAGE's development.
Clearly, these early advances in computers, software and networking that evolved from the SAGE system had a powerful impact on today's computers and the computer industry as a whole.
Page last updated: January 25, 2005 | Top of page
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