Vintage computers, part 2
Our retrospective last month on the school’s analog computer brought back memories from two alumni: Herb Lindberg (1957) and Di Chen (1959).

Pictured above is an analog circuit diagram from Lindberg’s thesis, “Studies of Second and Third Order Contactor Control Systems.” The physical manifestation of the diagram was “a tangle of wires that hung from [a] circuit board,” Lindberg says.

Here’s how he describes what it did: “The circuits were a simulation of a contactor (on-off or bang-bang) control system driving a second-order process (e.g., pitch of an aircraft). The three major parts of the circuits are labeled: 1) Controlled Process, 2) Switching Function, and 3) Time Delay. At this point I was studying the effects of switching time delay on the error e = x - y between a desired (input) state x and resulting (output) state y. The time delay circuit was an analog implementation of a Pade approximation to exp(-pT), where p is the Laplace variable and T is the simulated time delay.”

Di Chen’s choice for computing was to fire up the IBM 650 digital computer in Stanford’s Electronics Research Laboratory. The 650 was in high demand, but no picnic to work with, as he recalls:

“The IBM 650 computer was a vacuum tube computer, used hundreds of 12AUX type miniature vacuum tubes. The size of this computer was about that of a tall refrigerator, with a small chimney to exhaust the heat generated to the outside. There was a 2' x 2' wiring board with a mass of crisscrossing banana plug attached wires, custom configured for each project, which had to be plugged onto the computer. The main memory was a magnetic drum memory. As I recall, the diameter of the drum was about one foot and it was about 1 1/2' long. It made a loud humming noise when it was in operation, and the total memory was a few MBytes.

My project was written in assembly language, coded on punch cards, which were stacked in correct sequence, read by a desk-sized reader, one card at a time.

This computer was considered a state-of-the-art machine at that time, and was heavily used. As a lowly graduate student, the only time I could get on to that computer was after midnight. Often time, I could hardly keep my eyes open for the morning classes after a whole night of work on this marvelous machine.

“How time has changed.”

We are interested in your nostalgic photos and the stories they tell. If you’d like to share them with the Stanford Engineering community, e-mail them to David Orenstein, Manager, Communications and P.R.