Jay Forrester (Whirlwind and SAGE)

Jay Wright Forrester (1918-2016)
Jay Wright Forrester (1918-2016)

After high school, in 1936 Jay Forrester (1918-2016) enrolled in the Engineering College at the University of Nebraska to study Electrical engineering, and then in 1939 went to do graduate work at MIT on servomechanisms. He stayed at MIT until 1944 when he chose a Navy-sponsored program to design computers for testing new aircraft designs. (Most computer development during WWII and the postwar period was funded by the military, e.g. the ENIAC and Colossus projects.)

The program was initiated following a request from US Navy, asking the MIT Servomechanisms Laboratory to build an aerodynamic stability analyzer, which essentially was a primitive flight simulator. The pilot sat in a cockpit, pulled the joystick and the servos were supposed to respond in real-time to his actions. The problem was to get it all to work fast enough to give the pilot a realistic feel for the plane.

Initially, Jay Forrester and his group started building a large analog computer for the task but soon found that it was slow, inaccurate, and inflexible. Solving these problems in a general way would require a much larger system, perhaps one so large as to be impossible to construct. While thinking about the problems of fast analog computation Forrester heard (from a member of the MIT team, who saw a demonstration of ENIAC and suggested that a digital computer was the solution) about the digital computers being built by Mauchly and Eckert, and John von Neumann (ENIAC and EDVAC). He talked to Eckert and Neumann and was convinced that a fast digital computer, built by electronic valves, was what was needed. In early 1946 a digital computer project was started at the new laboratory, set up by Forrester, and speed was the absolute goal for this, what became known as the Whirlwind Project.

Whirlwind Computer

At first, Forrester planned to build a bit serial electronic computer like the EDVAC (EDVAC was a binary serial computer with automatic addition, subtraction, multiplication, programmed division, and automatic checking with an ultrasonic serial memory), but soon realized that this would be slow. A bit serial computer works by calculating one bit at a time. This allows the same hardware to be re-used during computation and so simplifies the design. The alternative is to use a bit parallel design that uses multiple copies of the basic hardware to compute an N-bit result in one operation. Bit parallel may be faster, but it needed so much more hardware that valve failure became a serious problem.
By 1947, Jay Forrester and his collaborator, the computer scientist Robert Everett (1921-2018) completed the design of a high-speed stored-program computer for this task—the Whirlwind. Construction of the machine started in 1948, an effort that employed 175 people, including 70 engineers and technicians. Whirlwind took 3 years to build and first went online on 20 April 1951. The project’s budget was $1 million a year, and after three years the Navy had lost interest. However, during this time the Air Force had become interested in using computers to help with the task of ground-controlled interception (the Cold War just began), and the Whirlwind was the only machine suitable for the task.

Forrester studied what made the valves fail after about 500 hours, which means regular breakdowns occurred and discovered that the cause was the silicon added to make the refining of the nickel easier. Silicon-free nickel cathodes increased the life of the average valve from 500 to 500000 hours. This discovery was a key factor, which made the Whirlwind possible.

The Whirlwind computer
The Whirlwind computer

Another remarkable innovation increased the reliability of the machine still further. The Whirlwind could alter the voltage on the grid of each valve to test for imminent failures.

Forrester had solved most of the problems in the design of Whirlwind but one remained—the memory. He realized that storage was the critical problem. The whole project depended on finding a more reliable and economical method of storage. At the time most memories were serial, as it was in Edvac. The first fast large memories were based on mercury delay lines that kept a serial stream of bits circulating as sound pulses. The Williams tube, used in the SSEM computer, was a faster version of the same principle. The speed of the original design of Whirlwind (20 KIPS) turned out to be too slow to be very useful, and most of the problem was attributed to the fairly slow speed of the Williams tubes for the main memory of 256 words. A CRT display tube formed a pattern of bits as spots of light which were recirculated using a photocell and feedback amplifier. It was faster but the tubes burned out far too frequently.

Initially Whirlwind used a modified form of the Williams tube. An additional flood gun maintained the pattern of dots while a writing gun was used to alter the pattern. Thirty-two such tubes were needed to provide the 4KBytes of storage that the Whirlwind needed. Given a tube life of one month and a cost of $1000, the running cost of the machine was very high, $1 per bit per month.

Magnetic core memory of An Wang

In 1949 Forrester started to think about ways of making a 2D or 3D form of storage rather than the one-dimensional recirculating method of storage represented by the delay line and Williams tube. After spending much time thinking about the problem, he encountered an article on the use of magnetic materials as amplifiers. He knew also about the pulse transfer controlling device of the Chinese engineer An Wang, which implemented write-after-read (essentially making magnetic core memory possible). Forrester ordered some of the material and built an array that passed current through rings of the material to magnetize it in one of two directions.

This worked but it was too slow. Then the breakthrough happened! Forrester came up with a scheme that involved threading rings of the magnetic material on an x-y grid of wires. Each ring or core was threaded onto a unique pair of x-y wires (see the nearby photo). A third read/write wire was threaded through all of the cores. To read or write a bit half of the current needed to change the magnetization of a core was placed on one of the x wires and on one of the y wires. Only the core at the intersection of the two wires was subject to a current sufficient to change its polarity. This enabled direct access to each bit in the array.

Initially, Forrester had doubts that it would work. Perhaps the repeated exposure to half the current needed to change the polarity would eventually cause a slow degradation in the state of the core. It didn’t and coincidentally current core memory worked! A special test bed computer was built just to verify the principle. Then in 1953 Whirlwind was equipped with a new core memory that doubled its speed (up to 40 KIPS), improved its reliability, and made it cheaper to keep running. In 1951 Forrester applied for a patent, which was granted in 1956 (see the US patent Nr. 2736880). After its debut in Whirlwind, magnetic core memory was used in computers until the beginning of the 1970s.

Jay Forrester is working on Whirlwind. The woman is working on the 16-inch Whirlwind Display Console.
Jay Forrester is working on Whirlwind. The woman is working on the 16-inch Whirlwind Display Console.

The Whirlwind was the fastest machine of his time. Its list of “firsts” is long and impressive but what really matters is the simple fact that the Whirlwind was the first computer capable of real-time computations. It could add two 16-bit numbers in two microseconds and could multiply them in twenty microseconds. Of course, the Whirlwind was huge but it only used 4000 valves, which was less than a quarter of the valves used in ENIAC—a much less powerful machine.

The instructions and data are entered into the memory by means of switches or with a perforated tape. As additional memory can be used a magnetic drum (8KB), as well as a magnetic tape device. Whirlwind was also the first computer, which used a graphical display (with a resolution of 256×256 dots).

The light pen of Whirlwind
The light pen of Whirlwind

Whirlwind was the first computer, which used a revolutionary new device—the light pen (see the nearby image), which will flourish in its successor—SAGE, to identify aircraft of interest by selecting them on the CRT. The light pen was developed in the early 1950s by a Lincoln Lab, in Lexington, MA. engineer—Robert R. Everett (an assistant of Forrester, who will play a major role in the SAGE project also), who was charged with the task to develop a device, to read the position of a dot on the screen of the Whirlwind computer for diagnostic purposes. The light pen sensed light on the CRT screen and caused a computer interruption to occur. This process occurred in just a few microseconds, but it was enough time that the computer could identify the specific graphical item that had been pointed to.

Forrester left the Whirlwind project in 1956 when it was running smoothly through its final stages, to devote his time to his next brainchild—the monstrous SAGE computer.

SAGE computer

The U.S. military SAGE Computer System, developed in the 1950s and operational by 1961, is beyond all doubt the largest, heaviest, and most expensive computer system ever built! SAGE was the brainchild of Jay Forrester and George Valley, two professors at MIT’s Lincoln Lab.

As early as 1948, Jay Forrester wrote a lengthy document containing his concept for a plan to improve America’s air defense using techniques learned from W.W. II radar development. The concept was first tested on his Whirlwind computer, connected to receive data from a long-range and several short-range radars set up on Cape Cod. The key breakthrough was the development of magnetic core memory that vastly improved the machine’s reliability, operating speed (×2), and input speed (×4) over the original Williams tube memory of the Whirlwind.

This is a small part of SAGE's CPU
This is a small part of SAGE’s CPU

After the advanced Whirlwind computer was completed and running, a design for a larger and faster machine (called Whirlwind II) was begun. But the design soon became too much for MIT’s resources. It was decided to shelve the Whirlwind II design without building it and concentrate MIT’s resources on the Whirlwind I. IBM, the prime contractor for the SAGE (so-called AN/FSQ-7) computer based the machine’s design more on the stillborn Whirlwind II design than on the original Whirlwind.

The SAGE name stood for “Semi-Automatic Ground Environment.” It was a continental air-defense network commissioned by the U.S. military, designed to coordinate radar stations and direct airplanes to intercept incoming planes. SAGE consisted of 23 direction centers (concrete-hardened bunkers across the United States and one in Canada), each with a SAGE computer that could track as many as 400 airplanes. The SAGE system was designed to detect atomic bomb-carrying Soviet bombers and guide American missiles to intercept and destroy them.

The total weight of the SAGE was over 250 tons. It contains 60000 vacuum tubes, 1750000 diodes, and 13000 transistors. The total system area was about 2000 square meters, the CPU occupied an area of 15 x 45 m, consoles area was 8 x 15 m. Architecture: duplex CPU (one of which would be in standby mode and one of which would be running), no interrupts, 4 index registers, Real Time Clock, Word Length: 32 bits. Performance: 75KIPS (single-address). The power consumption was about 3 Megawatts and specialized generators and cooling systems were required to support the computers.

• Magnetic core (4 x 64K word)
• Magnetic Drum (150K word)
• 4 IBM Model 728 Magnetic Tape Drives (~100K words each)
Note: Memory Cycle Time: 6 microseconds, all systems with parity checking

A SAGE operator in front of a CRT display, working with a light gun
A SAGE operator in front of a CRT display, working with a light gun

I/O devices:
• CRT display
• keyboard
• light gun
• punched card reader (IBM 713)
• card punch (IBM 723)
• line printer (IBM 718)
• realtime serial data (teletype, 1300 bps modem, voice line)

SAGE had more than 150 display consoles housing a 48-inch long Vector CRT, each equipped with a light gun pointing device, as well as a “Typotron” display tube, capable of displaying more than 25K characters per second.

SAGE was the most ambitious computer project ever undertaken, as it required over 800 programmers and the technical resources of some of USA’s largest corporations—IBM (hardware), Burroughs (inter-Center communications), MIT’s Lincoln Laboratories (system integration), Western Electric (design and construction of buildings) and SDC (part of the RAND Corporation) for software. The total project cost is estimated to have been between 8 and 12 billion dollars. The SAGE system remained in continuous operation until 1983, over 20 years

Biography of Jay Forrester

Jay Wright Forrester (1918-2016)
Jay Wright Forrester (1918-2016)

Jay Wright Forrester was born on 14 July 1918 and grew up on a cattle ranch in Anselmo, Nebraska, USA, to Ethel Pearl Wright Forrester (1886-1958) from Hastings, Nebraska, and Marmaduke (Duke) Montrose Forrester (1883-1975), from Emerson, Iowa. Jay had a sister, Barbara Francis (1921-2009). Both his parents attended Hastings College, in Nebraska. When they arrived in Anselmo around 1910, both worked as country schoolteachers. Duke was also a Nebraska state legislator for several terms.

Jay was taught at home by his mother for his first two years of schooling. After that, he rode his horse one and a half miles to a one-room schoolhouse. There, for the first two years, he was taught by his father. Jay developed an early interest in electricity, tinkering with doorbells, batteries, and telegraphs. While in a local high school, he built a wind-driven, 12-volt electrical system using old car parts, and it gave the ranch its first electric power. He was offered a scholarship to an agricultural college but decided that the life bucolic was not for him and, instead, enrolled in the University of Nebraska to study electrical engineering.

After earning a bachelor’s degree in electrical engineering in 1939, Jay moved to MIT, where he worked as a research assistant with Gordon Stanley Brown (1907-1996), a professor of electrical engineering and pioneer in servomechanism theory and applications. During World War II, Forrester worked on feedback control systems and servo-control systems for radar. For his master’s thesis, he designed and built a servo to stabilize radar antennae on naval ships. In 1943, the prototype was installed on the aircraft carrier Lexington and Jay subsequently traveled to Pearl Harbor to ensure its continued functioning. Though a civilian, he volunteered to stay on board when the fleet was ordered to sea to make sure the servo (and thus the ship’s radar) worked. During the mission, Lexington participated in the retaking of the Marshall Islands and survived a torpedo strike.

Jay Forrester holding a 64x64 core memory plane, 1954
Jay Forrester holding a 64×64 core memory plane, 1954

Jay received an S.M. degree in Electrical Engineering from MIT in 1945. Later, he was a professor at the MIT Sloan School of Management (since 1956), where he introduced the Forrester effect describing fluctuations in supply chains and is credited as the founder of system dynamics, which deals with the simulation of interactions between objects in dynamic systems and is most often applied to research and consulting in organizations and other social systems. In 1972, he received the IEEE Medal of Honor, the IEEEs highest award. In 1982, Forrester received the IEEE Computer Pioneer Award. In 1995, he was made a Fellow of the Computer History Museum “for his perfecting of core memory technology into a practical computer memory device; for fundamental contributions to early computer systems design and development”. In 2006, Jay was inducted into the Operational Research Hall of Fame.

Besides the Whirlwind computer, Forrester’s most notable contributions include the following:
“Multi-coordinate digital information storage device,” the precursor to Random Access Memory (RAM);
He is believed to have created the first animation in the history of computer graphics, a “jumping ball” on an oscilloscope.
The reinterpretation of world dynamics through computer simulations of the Earth’s natural systems (e.g. natural resources, climate, etc.) in interaction with human-created systems (e.g. cities, nations, industries, etc.).

In 1989, Forrester received the National Medal of Technology, the nation’s highest award for technical achievement from George Bush
In 1989, Forrester received the National Medal of Technology, the nation’s highest award for technical achievement from President George Bush

On 27 July 1946, Jay Forrester married Susan Swett (1917-2010) from Southern Pines, Moore County, North Carolina. They had a daughter, Judith, and two sons, Nathan Blair (born 1950), and Ned Cromwell. Both his sons have continued his MIT legacy, Ned studied electrical engineering, and Nathan focused on system dynamics.

Prof. Jay Wright Forrester, founder of the field of system dynamics, and a pioneer of digital computing, considered by some people to be one of the greatest minds of the last 100 years, died on 16 November 2016 (aged 98) in Southern Pines, Moore County, North Carolina, USA.