It’s hard to imagine daily life without a home computer playing at least a small part in the day’s activities. Whether it be for work or fun, laptop and desktop computers are integral to the way we regularly function on a day-to-day basis. Of course, it wasn’t always this way. The desktop computer had to go through a long line of changes and innovations to get where it is today. One such change came in the form of Edmund Berkeley’s invention, the Simon Electronic Brain. But what was this so-called Electronic Brain, and how did it work? What was its significance to the history of the home computer? Let’s discuss the details.

Edmund Berkeley shows the operation process of the Simon electronic brain.

Three Facts about the Simon Electronic Brain 

  • Edmund Berkeley’s first personal computer, the Simon Electronic Brain, sold for just $600 in 1950 — a price that seems just as unheard of today as it was over 70 years ago.
  • It’s not enough that Berkeley’s “giant brains, or machines that think” were credited as the first personal computers — he also had the foresight to predict that, one day, we might have small desktop computers in the home that draw their power from power lines like an appliance.
  • Because the Simon Electronic Brain only had two bits of memory, the computer wasn’t actually capable of doing any serious, practical computing. It was much closer to a proof of concept than an actual, significant device. 
1951 magazine clip

Simon Electronic Brain History

After several life-changing encounters with computers — first in 1939, when he visited Bell Laboratories to see George Stibitz‘s Complex Number Computer; second in 1942, when he joined the U. S. Navy and worked at Dahlgren Laboratory as a mathematician, observed Mark I, and worked on the construction of the next sequential calculator project (Mark II); third in 1946 when he drafted a specification for one of the first UNIVAC computers — American computer scientist, publisher, and anti-nuclear activist Edmund Berkeley became an independent consultant and founded his own company, Berkeley Associates.

Quick Facts

Edmund Berkeley
Original Use
First personal computer

Shortly after this, in 1949, Berkeley wrote one of the first books on electronic computers for a general audience. This is the thing that made him famous. Titled Giant Brains, or Machines That Think, Berkeley’s book first described the principles behind computing machines before giving a technical but accessible survey of the most prominent examples of the time — including machines from MIT, Harvard, the Moore School, Bell Laboratories, and elsewhere. To conclude, Berkeley made several pertinent predictions for the future of the computer and then outlined the details of his computing machine: the Simon Electronic Brain.

Plans on how to build this electronic brain — in addition to a general description of the computer’s state of the art technology — were published in a series of 13 consecutive articles in the journal Radio Electronics, starting with the October 1950 issue. The first working model was built by William A. Porter, a skilled mechanic, Robert A. Jensen & Andrew Vall, two Columbia University graduate students of electrical engineering. Porter did the basic construction, then Jensen and Vall took the machine and made it functionally sound. They did this through a series of improvements to Berkeley’s concept, including the design of a switching system that made follow-through possible, the set-up of an automatic synchronizing system, the installation of a system for indicated errors due to loss of synchronization, and a complete re-design of the machine’s power supply.

Black and white photo of the Simon electronic brain.

Simon Electronic Brain: How It Worked

The Simon computer was a relatively simple piece of technology, containing 129 relays (which were readily available at various local army surplus stores at that time), a stepping switch, and a five-hole paper tape feed. Simon’s program was executed directly from this five-hole paper tape feed. The Simon computer’s program instructions and data were input via a five-level paper tape reader — one level for each of the five holes on the paper tape feed — as well as a standard five-level paper tape. This was intended for use with teletypes before the advent of ASCII character codes. Data could also be input manually to the Simon computer during program execution through the use of the front-panel switches.

Various registers were provided with this early home computer — some for general data storage, others for targeted purposes. The registers and busses were a mixture of two and four bits wide. The processor (ALU) was also two bits wide. Output was via the five lamps, which were connected to the output registers.

All of this tech amounted to just a handful of simple functions: Addition, negation, greater than, and selection. As it turned out, these so-called “giant brains, or machines that think,” were much less capable than a real, human brain. Still, even just these basic mathematical functions were revolutionary for the time. 

To program Simon, one had to prepare a paper tape with machine instructions and data. The paper tape functioned as the program memory. Simon executed the program instructions as it read the tape, but it did not load the program. The tape reader read in one direction only, which meant that all instructions on the tape were executed in sequence — in other words, no skipping instructions. (Some degree of conditional operation was provided by the selective assignment function of the ALU. There was also a single opportunity to create a program loop by simply forming the entire program tape into a loop.)

1955 newspaper clip.

Simon Electronic Brain: Historical Significance

Beyond the sheer importance of being regarded by many as the first personal computer, the Simon Electronic Brain established at least half a dozen world records at the time (including being the smallest computer in existence). It was the very first shot at making an affordable home computer for educational purposes. While there were various other large-scale projects in the works at the same time as the Simon Electronic Brain, Berkeley’s creation is widely considered to be the leader of the pack. Not to mention, the Simon Electronic Brain also introduced the technological principles of binary arithmetic, computer logic, and automatic computing to the general public. While only 400 Simons were sold by 1959, the Electronic Brain-inspired such pioneering computer scientists as Ivan Sutherland, who then went on to develop even more groundbreaking personal computers.

Simon Electronic Brain Explained — Everything You Need To Know FAQs (Frequently Asked Questions) 

What was the Simon Electronic Brain?

The Simon Electronic Brain was the first personal home computer.

How did the Simon Electronic Brain work?

The Simon Electronic Brain worked via 129 relays, a stepping switch, and a five-hole paper tape feed. The paper tape functioned as the program memory.

Who invented the Simon Electronic Brain?

The Simon Electronic Brain was invented by Edmund Berkeley, who detailed his “giant brains, or machines that think” in a series of articles and a book that preceded its invention.

When was the Simon Electronic Brain invented?

The Simon Electronic Brain was invented in 1950.

Is the Simon Electronic Brain still used?

The Simon Electronic Brain isn’t used anymore today, but the revolutionary technology introduced by the technology helped to shape computers as we know them today.

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