July 7, 1949 — The First Program Using Electrostatic Memory Was Run

One of the most underrated milestones in computing history. This was the moment when the fundamental principle behind computer RAM first proved itself in practice—the same principle our computers still rely on today.

Before electrostatic memory, computers used much slower and far more complicated storage technologies, such as mercury delay lines and magnetic drums. Their performance depended on mechanical processes and physical movement, making them far too slow for the kind of high-speed memory computers would eventually need.

On July 7, 1949, engineers at MIT ran a program on the Whirlwind computer using electrostatic memory. The program ran error-free for one hour and fifteen minutes.

Here’s a simplified explanation of how Whirlwind’s electrostatic memory worked:

Step 1. Inside the tube were an electron gun and a screen. The gun could aim a narrow electron beam at any point on the screen. When the beam struck a particular location, it changed the electrical charge at that spot.

Step 2. The impact created a small difference in electrical potential at that location. That difference represented a single bit of information.

Step 3. To read the bit, the electron beam returned to the exact same location and struck it again. Behind the screen was a metal pickup plate. This second strike changed the stored charge, producing a very brief electrical pulse on the plate. After being amplified, the shape of that pulse revealed which bit had been stored before the second strike.

Step 4. The bit then had to be rewritten. Once it had been read, the original charge pattern was considered destroyed. To preserve the data, the system immediately aimed the electron beam back at the same location and recreated the bit.

Yes, the computer had to keep rewriting the stored data continuously to prevent it from disappearing. That’s why it’s called volatile memory—it only exists while power is supplied.

As surprising as it sounds, modern RAM works in much the same way. Data is still stored as an electrical charge, and it still has to be refreshed continuously. The difference is that today’s memory stores the charge in tiny capacitors instead of a cathode-ray tube, and uses transistors instead of an electron gun.

The Whirlwind project was led by Jay Forrester, who a few years later invented magnetic core memory. It replaced electrostatic tubes and became the standard form of computer memory throughout the 1950s and 1960s.

The successful run on July 7, 1949, was one of the earliest practical demonstrations of high-speed random-access memory—a technology without which no modern computer could exist.

See also 7 июля 1949 — запущена первая программа на электростатической памяти.