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Dr. Strangelove Meets IBM: The SAGE System


History of Computing: Dr. Strangelove Meets IBM: The SAGE System

History of Computing #1


How many programmers are there in the world today? It may be difficult to believe, but at one time, 20 percent of the world's programmers were working on a single project. The year was 1953 and this mammoth task was known as the SAGE system—a continental air-defense network commissioned by the U.S. military. Over the course of its ten-year development, SAGE (Semi-Automatic Ground Environment) was the most ambitious computer project ever undertaken, one that occupied over 800 programmers and the technical resources of some of America's largest corporations. Strangely enough, few people in the computer business now even know it existed.

What was SAGE?

Born of cold war hysteria and a military-industrial-academic complex, SAGE was the brainchild of Jay Forrester and George Valley, two MIT professors at that school's Lincoln Lab. SAGE project development was a strange affair, the outgrowth of a flight simulator project that used first analog, then digital, computing techniques. As project funding and goals changed, Forrester and his military backers underwent a process of mutual alignment to keep some kind of digital computing expertise alive.

Spec Sheet for SAGE (A/N FSQ-7)

Architecture: duplex CPU, no interrupts, 4 index registers, Real Time Clock

Word Length: 32 bits

Memory: magnetic core (4 x 64K word); Magnetic Drum (150K word); 4 IBM Model 729 Magnetic Tape Drives (~100K words ea.); all systems with parity checking

Memory Cycle Time: 6us

I/O: CRT display, keyboard, light gun, realtime serial data (teletype, 1300 bps modem, voice line)

Performance: 75KIPS (single-address)

Technology: vacuum tube (60,000); diode (175,000); transistor (13,000)

Size: CPU (50 x 150 feet, each); consoles area (25 x 50 feet)

Weight: 250 tons (500,000 lbs)

Power Consumption: 3 Megawatts (enough to supply 2,000 average American homes)

It has been said that technology is politics by another name. While this is a strong claim that needs to be applied on a case-by-case basis, what became SAGE was the result of momentous political events, to which SAGE was seen as a technical solution. Specifically, the Berlin crisis (1948), the Soviet testing of an atomic bomb (1949), the Korean War (1950), the Soviet detonation of a hydrogen bomb (1953), the launching of Sputnik (1957), and the increasingly ideological cast of two world systems of government seemingly converging towards unavoidable conflict, drove SAGE system planners and politicians to conceive of a "shield" against the "Red Menace."

In a long 1948 report, Forrester laid out a plan to improve America's air defense using techniques learned from W.W. II radar development (MIT had become the center of that field's development). After many fits and starts, changes in project direction and focus, the system that emerged was composed of 23 concrete-hardened bunkers across the United States (and one in Canada) linked into a continental air-defense system. SAGE would detect atomic bomb-carrying Soviet bombers and guide American interceptors to destroy the invaders. It could also be linked to nuclear-tipped Bomarc and Nike missiles.

Each of the 23 SAGE "Direction Centers" housed a computer (known as the "A/N FSQ-7") that consumed 3MW (megawatts!) of power, had approximately 60,000 vacuum tubes, and took over 100 people to operate. The total project cost is still classified, though it's estimated to have been between 8-12 billion 1964 dollars, many times the cost of the Manhattan Project that developed atomic weapons initially. Four main contractors were responsible for SAGE: IBM for hardware; Burroughs for inter-Center communications (modems); MIT's Lincoln Lab (later MITRE Corporation) for system integration; Western Electric for design & construction of buildings; and SDC—a spin-off of the RAND Corporation—for software.

The first SAGE Direction Center came online in November of 1956, the last in 1962. When the final SAGE Direction Center was dismantled (the Canadian one mentioned previously, in 1983), its technical advances, now seen in historical perspective, seemed even more remarkable. Here are some of the highlights:

  • The invention and deployment of the modem so that all the Direction Centers were linked and shared data about their immediate situations across airspace sectors.
  • Core memory, what all computers used as primary high-speed, random-access memory from 1953 until the mid-1970s, was invented by Jay Forrester for SAGE's precursor machine, the "Whirlwind I."
  • SAGE ran the largest single piece of code then ever written: a real-time executive that was a then-unimaginable 500,000 lines.
  • At a time when vacuum tube computers were down for maintenance about 1 month per year, SAGE was off-line for only 1 to 10 hours a year.
  • Extensive development of A/D and D/A conversion techniques
  • The "COMPOOL," an area in system memory that could be shared by various subroutines, was invented and developed for SAGE. The COMPOOL would re-emerge as a crucial concept in COBOL.
  • What we now call multiprocessing, real-time database management, distributed processing, timesharing, interactive displays, and networking were used extensively.
  • "Marginal checking," a testing technique allowing early detection of components likely to fail
  • Memory "cycle-stealing"
  • Buffered I/O
 
Official USAF photo showing radar technician using light gun at SAGE console.

At a recent lecture on the SAGE system held at The Computer Museum History Center, project engineer Les Earnest (now a research scientist at Stanford University) somewhat sarcastically called SAGE "a great peacetime defense system." Earnest was alluding to the fact that by the time the last Direction Center came on-line in 1962, the ICBM (rather than a bomber) had become the main threat—a threat SAGE was unable to counter given its operating speed. Like ENIAC before it, SAGE did not meet its overall system objectives yet greatly advanced the state-of-the-art in computing by training a generation of hardware and software people in digital techniques.

Jim Wong, a software engineer on the SAGE project notes: "'It was first done in SAGE.' For many, many years those were the words said in industry. SAGE was the real-time, command and control computer-based system with capability so advanced that 40 years later, today, some of that capability can still be called state of the art."

Along with training a generation of computer people, the SAGE project also brought in some $500 million for IBM, the principal contractor. It is possible that without this source of revenue, IBM may not have had the financial strength, or even technical know-how, to develop the System/360 series of computers—the single most successful computer architecture of all time (over $100 billion worth of systems). SAGE also laid the groundwork for the SABRE airline reservation system and SAGE technologies were deployed in the U.S. air traffic control system as well.

The sheer size of the SAGE computer inspires a deep appreciation for the technical virtuosity and sheer will to succeed embodied in this machine. It is sobering to realize that a Palm handheld has more computing power. The computing pioneers before us faced almost insurmountable technical, economic, and managerial obstacles, yet they persevered, and in the process invented many of the architectural, component, and software technologies that we continue to use to this day.


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