Mainframer Recalls Helping Create the FAA System

IEEE Lifetime Fellow Claud M. Davis shares his experience architecting the System/360

Great achievements in history can often be attributed to a person’s desire for fame, fortune or power. In other cases they are achieved by one’s drive to meet a challenge or accomplish something that has never been done before. IEEE Lifetime Fellow Claud M. Davis falls into the latter category and was part of the team that architected both the System/360 and the first computer-aided air traffic control system. Not searching for any credit, Davis says he was just rising to the challenge. “I’ve had a great career,” he remarks. “Engineers always like a problem to solve and IBM offered me a challenging problem every year.”


Davis was one of 12 engineers who designed the original System/360 architecture. He said he was about to take a job in the lab when he got a call from Bob Evans, Vice President Data Systems Division, and Systems Development Manager of the Poughkeepsie Lab, who didn’t think the job was the best use of Davis’ skills. “He called me into his office and said, ‘You’re now working for Fred Brooks.’” Brooks, Manager 360 Development, was lead for the team composed of representatives from the collaborating Laboratories: Poughkeepsie, N.Y., Endicott, N.Y. and Hursley, U.K. This team produced the 360 architecture and determined the five 360 models that made up the IBM product line: the 30, 40 and 50, which shipped in April 1964, and the 60 and 70 which shipped at a later date—renamed as models 65 and 75.

Davis and the team took advantage of IBM’s new Solid Logic Technology (SLT) where multiple circuits were put onto a single ceramic chip, which resulted in greater speed and smaller size. This allowed the engineers to put a very powerful machine in a very small space. “Until then we had to use very large boxes. We laughingly said the size was determined by what would fit in the elevator, but that was more folklore than truth,” Davis remarks. The solid-state technology developed for the 360/Systems was a major step in technology. The concept of using multiple circuits on a ceramic chip is still employed today.

Brooks’ team began work on new architecture that would be compatible both in software and hardware, cover both scientific and commercial computation and span the total IBM product line. In order to accomplish this, many issues had to be resolved, as the present seven-bit byte of information didn’t allow for growth and checking. Richness of function of the instruction set and speed of the I/O attachment had to be resolved between the high-end and low-end of the line. Many trade offs were made as part of this resolution, but ultimately Brook and his team achieved their goal.

Davis’ next role was to lead and manage the design and model build of the Federal Aviation Administration’s (FAA’s) computer-aided air traffic control system. MIT Lincoln Labs originally drew up specifications for the project—a book three to four inches thick. Davis recalls, “One Friday afternoon Peter Fagg, 360/Systems, Hardware Development Manager, dropped it on my desk and said he’d like to know by Monday morning if it could be built. I replied on Monday, ‘Yes, it can be built with present technology.’ Fagg said four engineers in the lab already said it couldn’t be done. I responded, ‘I think that’s right: If they believe they can’t do it, they can’t, but I can.’ Then Peter said you are in charge of this one.” Davis led a small team of engineers who designed the hardware for the system, which was delivered to the FAA in 1965. The same basic architecture is used today.

Davis says the toughest thing was to guarantee the machine wouldn’t fail more than once a year, at a time when normal commercial machines were failing once a month. To develop a system that would fail softly, the team used 16 independent memories and seven processors; four were used for processing and the other three were used as channels. Davis says. “The design provided for one processor to take over another failing processor’s workload without interruption. This was accomplished through a new design where vital information was being reflected into memory.” He adds “It was with the FAA project IBM learned to use multiple machines efficiently.”

The most important thing IBM learned from FAA project, from a commercial perspective, was the ability to do remote servicing. IBM could, for the first time, service a machine anywhere in the world by cycling the machine and comparing patterns with correct data. Davis recalls. “We knew the pattern you were supposed to have, and if it wasn’t a match, you located the trouble and were able to fix it. Repair time was down to 30 minutes.”

Davis was inducted as an IEEE (Institute of Electrical and Electronics Engineers, Inc.) Life-time fellow in 1983 for his work with the FAA, architecting and developing this large, fault-tolerant computer system for air traffic control. He later received the IEEE’s Simon Ramos award in 1993 for leadership in the pioneering development of computer-aided air traffic control systems.

“I’ve had a very fulfilling engineering career. It was exhilarating, to say the least. These were my two most important projects,” he says. “As far as the machines, I feel technology has carried us at a breakneck speed.” Davis retired in 1989 after nearly 40 years with IBM, but says he still likes to solve a good problem. Now 84 years old, his recent challenges include keeping up with two adult children and three grandchildren. He has become an avid New England sports fan and attends games whenever possible, otherwise watching on TV. His son still thinks his father can fix anything and gives him many opportunities to use his skills.


Natalie Boike is a former IBM Systems Magazine managing editor.

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