The insides of a vacuum tube computer

1950s Vacuum Tube Computer Replica Communicates Through USB

When we talk about a “computer” today, we generally picture an electronic machine that can perform various kinds of mathematical operations, manage its program flow, move data from one place to another, and string all these functions together to perform some useful task. But once upon a time there were machines that could perform only a subset of these functions; these might be classified somewhere between computers and calculators.

One such machine was the Elektronensaldierer ES 24, built in 1955 by German computer pioneer Heinz Nixdorf. Its name translates as “electronic balancer”, with “balance” in the accounting sense meaning the difference of assets and liabilities. Designed to interface with a punch card machine from French manufacturer Bull, it contained several hundred vacuum tubes and could be used to add and subtract numbers stored on those punch cards.

[Henry Westphal] decided to make a modern copy of the ES 24 (translated), based on Nixdorf’s original schematics, for display in the HNF computer museum in Paderborn. The result is a huge display containing 204 tubes as well as a massive power supply. Like the 1955 original it can add incoming numbers and output the result as a twelve-digit decimal number. To make its inner workings visible, [Henry] also added a status light to each tube, showing whether it is storing a “0” or a “1”. This makes for a beautiful Blinkenlights display that shows the bits moving through the machine’s inner circuits.

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Inside Mechanical Calculators

For as busy as things can get at the grocery store on a typical afternoon just before the dinner hour, at least the modern experience has one thing going for it: it’s relatively quiet. Aside from the mumbled greetings and “Paper or plastic?” questions from the cashier, and the occasional screaming baby in the next aisle, the only sound you tend to hear is the beeping of the barcode scanner as your purchase is tallied up.

Jump back just 40 years and the same scene was raucous, with cashiers reading price tags and pounding numbers into behemoth electromechanical cash registers. Back then, if you wanted help with any arithmetic with more than just a few operations, some kind of mechanical calculator was your only choice. From simple “one-banger” adding machines to complex analog computers, mechanical devices were surprisingly capable data processing tools. Here’s a brief look at how some of the simpler ones worked.

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Retrotechtacular: Pascal Got Frustrated At Tax Time, Too

While necessity is frequently the mother of invention, annoyance often comes into play as well. This was the case with [Blaise Pascal], who as a teenager was tasked with helping his father calculate the taxes owed by the citizens of Rouen, France. [Pascal] tired of moving the beads back and forth on his abacus and was sure that there was some easier way of counting all those livres, sols, and deniers. In the early 1640s, he devised a mechanical calculator that would come to be known by various names: Pascal’s calculator, arithmetic machine, and eventually, Pascaline.

The instrument is made up of input dials that are connected to output drums through a series of gears. Each digit of a number is entered on its own input dial. This is done by inserting a stylus between two spokes and turning the dial clockwise toward a metal stop, a bit like dialing on a rotary phone. The output is shown in a row of small windows across the top of the machine. Pascal made some fifty different prototypes of the Pascaline before he turned his focus toward philosophy. Some have more dials and corresponding output wheels than others, but the operation and mechanics are largely the same throughout the variations.

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Binary Adder Will Give You Slivers


A while back we looked at [Matthias’] one-pin dot matrix printer. Now we’re jumping over to his woodworking website to feast on his wooden binary adding machine. His creation uses glass marbles as the data for this device. A resolution of up to six bits can be set on the top of the adder, then dropped into the machine as one number. With each new drop, the number is added to the total stored in the machine. The device is limited to totals less than 64. If a larger number is enter, the device wraps around back to zero by dumping the 7th bit off the end. He’s even got a master clear that allows you to easily read the stored total and evacuate the “data” from the machine.

This has quite a few less wires than the last binary adder we looked at… wait, it has no wires! But we still love it. A physical representation of what is going on with binary math really helps grasp what the magic blue smoke inside those silicon chips is all about. Don’t miss his video walk through of the adding machine embedded after the break. Can’t get enough of marbles interacting with wood? He’s got a few more projects you might enjoy. Continue reading “Binary Adder Will Give You Slivers”