Powering Up A Pluggable Module From The 1948 IBM 604 Electronic Calculator

June 8, 2026 by Maya Posch 2 Comments

In that awkward transition phase between electromechanical accounting systems used in the 1940s and the introduction of fully digital computers we find systems such as the IBM 604 Electronic Calculator, advertised for accounting, calculating and engineering tasks. While not capable of complex instructions, loops and other advanced features, it did use an interesting modular architecture with easily swappable modules containing a vacuum tube and associated components. Recently [Ken Shirriff] took a poke at one of these and even powered it up.

This kind of pluggable system would become a staple of computer systems, as they enabled the use of modules or cards with specific functions that could be swapped and combined at will to increase system flexibility, lower costs and make repairs a snap. For the IBM 604 a total of about 1250 vacuum tubes were used, apparently all of which were found on these pluggable modules.

The module that [Ken] got his hands on has a thyratron tube, which is effectively a high current switch and rectifier. In the short demonstration video you can see it being used to switch a lamp on and off, with further details explained in the article.

Despite being rather limited in its functionality and limited by the punch card input and output speed, the IBM 604 was still a smashing commercial success with over 5600 units produced. A transistorized prototype version with 2200 transistors and 95% less power usage was created in 1954 that formed the basis for the IBM 608, the world’s first commercial all-transistorized calculator.

The 608 didn’t last too long, however, as at that point the breakneck pace of semiconductor technology meant that any newly released product was already obsolete by the time it hit the market. Despite this, fundamentals like pluggable modules would keep showing up over and over, ranging from the 1950s Bendix G-15 to even modern day systems, including PCs with pluggable RAM and expansion cards as well as mainframes where hot swapping of even entire CPU modules is just another feature.

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Remember When Flash Drives Were Going To Make Your PC Faster?

May 26, 2026 by Zoe Skyforest 46 Comments

The 2000s was a decade of great change in the computer industry. The world had grown accustomed to corruptible floppy disks, blue screens of death, and achingly slow load times. In a few short years, all of that would change, as USB drives, better operating systems, and faster processors brought forth a new age of stability and speed.

Amidst this era of upheaval, Microsoft introduced a new technology. It was intended to increase performance on the cheap to a new generation of machines, but it would turn out to be little more than a gimmick that never really caught on. Let’s explore the easily-forgotten legacy of ReadyBoost.

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The Email Of The Future In 1986

May 24, 2026 by Jenny List 26 Comments

With so many online messaging services to choose from it’s almost as though the daddy of them all, email, has faded into the background as something you only use for more formal contacts. But it’s still the underpinning of much of the business world’s electronic communication and is likely to stay so for the foreseeable future. The BBC Archive takes us back to a time when email was relatively new, when in 1986 [Lesley Judd] takes a very chunky 1980s laptop on a plane from London to the Netherlands, and sends an email to her colleague at home using a payphone and an acoustic coupler.

There are so many of-their-era quirks in this film it’s difficult to pick, but little things like the aircraft still having smoking and non-smoking areas, there being no sign of a mobile telephone, or the payphone operating in Guilders rather than Euros make it from a different time. Perhaps most interesting though is the email system in use, because this isn’t an internet based service. Instead it’s using Telecom Gold, which was the UK telco BT’s online service offering to businesses, and part of the international Dialcom network. This was a commercial service which hung on until some time in the 1990s when the Internet finally displaced it.

The British writer L. P. Hartley used the phrase “The past is a foreign country; they do things differently there” as the opening sentence of one of his books, and the film below the break certainly brings that to mind. It’s a time that’s within reach, yet the changes in information technology over even the next decade or so would make the tech depicted not just obsolete but almost unrecognizable. Most of us today could sit at a 1996 laptop and send an email, but few of us would be as immediately at home with Telecom Gold.

It’s still possible to use an acoustic coupler today though.

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Spy Tech: A Quiet Radio For Spies

May 20, 2026 by Al Williams 9 Comments

Normally, when you think of a radio transmitter, you want the strongest signal and range. But if your radio operator is secretly operating as a spy, broadcasting their position isn’t a feature; it is a liability. This fact didn’t escape World War II radio designers.

In late 1942, the British realized they needed a way for Special Operation Executive agents, resistance members, and other friendly forces to communicate with an aircraft without attracting undue attention. Two engineers from the Royal Corps of Signals developed a pair of transceivers — the S-Phone — operating around 380 MHz just for this purpose. Frequencies this high were unusual at the time, which further deterred enemy detection.

The output power was below 200 mW, and the ground equipment consisted of a dipole strapped to the operator. No transistors, so with rechargable batteries, the rig weighed about fifteen pounds and reused some parts of a paratrooper radio, Wireless Set Number 37. The other side of the connection was installed in an airplane.

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Building A Working Replica Of The Chernobyl Power Plant’s SKALA Display

May 18, 2026 by Maya Posch 3 Comments

In a recent video by the [Chornobyl Family] it’s shown how they made the SKALA status display which was featured at the recent 40-year memorial exhibition of the Chornobyl Nuclear Power Plant (ChNPP) #4 reactor accident, along with the RBMK reactor control panel replica and SKALA console which they had made previously.

We previously covered this SKALA control system of the ChNPP’s RBMK reactors, as well as its 1990s modernization. This SKALA status display is one of the original elements of the control room, providing a status overview of the entire control system at a glance, including its processors and peripheral devices.

The replica uses similar looking components, with a metal casing and LED lighting that invokes the aesthetics of the original electroluminescent mnemonic panels. Overall the goal was to keep the appearance as close to the original as possible — they even had operators of the ChNPP reactors look over the panel and give it their stamp of approval.

Some of the components like the error indicators had to be 3D printed, while the metal case was cut out of sheet metal. There’s also a very big speaker for the alarm, at the top right of the panel. Along with the LEDs for the electroluminescent-style indicators this meant a lot of addressable LEDs and a lot of wiring.

The full build plans are available via the [Chornobyl Family] Patreon, if you feel like building up your own RBMK-style reactor control room.

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Inside The Heathkit Factory

May 15, 2026 by Al Williams 17 Comments

If you are a certain age, you doubtlessly remember Heathkit. They produced a wide array of electronic kits that were models of completeness and clear instructions. They started with surplus war parts in 1947 and wound up a major player in ham radio and early personal computers. But they made so many other things like TVs, radio control planes, and test equipment. All of it was made for you to build yourself. [Unseen History] released a video with the story of Heathkit from the start to the finish.

The company started out building kit airplanes, but after the war, they built a kit for an oscilloscope using military surplus. The less than $40 scope was still pricey in 1947 when a pound of bacon sold for 64 cents. But a “real” oscilloscope at the time would cost at least $400. The rest is history.

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Testing Giant Fire Darts From The Mary Rose

May 13, 2026 by Maya Posch 10 Comments

Fire arrow versus the recreated fire dart. (Credit: Tod's Workshop, YouTube) — Fire arrow versus the recreated fire dart. (Credit: Tod’s Workshop, YouTube)

The Mary Rose was a carrack in the English Tudor Navy of King Henry VIII that fought in multiple battles during the 16th century before it was sunk in 1545. After its wreck was located in 1971 and raised in 1982 the ship and all the items contained within the partially preserved hull became the focus of intense study. Among these items are the weaponry found, including the cannons, but also massive darts that seemed to have been designed for an incendiary payload. Recently [Tod’s Workshop] collaborated with others to test these presumed incendiary darts.

Although fire arrows have been around for a while, seeing what appears to be super-sized versions of these is somewhat unusual, but could make sense in taking out enemy ships of the time. The main questions are how you would even fire them, and how effective they would be. Were the darts thrown by hand from e.g. the crow’s nest, or fired from a cannon?

The reproduction darts used are based on the recovered remnants of the original darts, with an incendiary mixture inside a pitch-covered cloth covering. This mixture would be ignited by wooden fuses after a set amount of time, at which point the resulting fire would be basically impossible to put out. Obviously, this also means that if you were to throw one of these darts, it can absolutely not fall onto your own ship.

First tested was throwing the dart by hand, which seems like it would clear the ship. Of course, the three recovered darts were found near a rather special cannon that appeared to be both a miscast and angled upwards. Whether that cannon was used for launching apparently somewhat experimental darts is hard to say, but it can be tested. Sadly, lacking a full-sized black powder cannon a scale model dart was fired using compressed air.

From that scale test it’s clear that at full charge the dart would disintegrate due to the rapid acceleration, but a ‘soft’, or reduced, charge could work against nearby targets. Once the dart lodges itself into the enemy ship’s structure, it would definitely cause severe damage as further tests in the video demonstrate. Having a salvo of these fire darts fired at you from a nearby ship would definitely make for a pretty bad day.

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