Once upon a time, when the earliest spy satellites were developed, there wasn’t an easy way to send high-quality image data over the air. The satellites would capture images on film and dump out cartridges back to earth with parachutes that would be recovered by military planes.
It all sounds so archaic, so Rube Goldberg, so 1957. And yet, it’s still a viable method for recovering big globs of data from high altitude missions today. Really, you ask? Oh, yes indeed—why, NASA’s gotten back into the habit just recently!
The 1970s was a somewhat awkward phase for the computer industry — as hulking, room-sized mainframes became ever smaller and the concept of home and portable computers more capable than a basic calculator began to gain traction. Amidst all of this, two interpreted programming languages saw themselves being used the most: BASIC and APL, with the latter being IBM’s programming language of choice for its mainframes. The advantages of being able to run APL on a single-user, portable system, eventually led to the IBM 5100. Its story is succinctly summarized by [Bradford Morgan White] in a recent article.
The IBM PALM processor.
Although probably not well-known to the average computer use, APL (A Programming Language) is a multi-dimensional array-based language that uses a range of special graphic symbols that are often imprinted on the keyboard for ease of entry.
It excels at concisely describing complex functions, such as the example provided on the APL Wikipedia entry for picking 6 pseudo-random, non-repeating integers between 1 and 40 and sorting them in ascending order:
x[⍋x←6?40]
Part of what made it possible to bring the power of APL processing to a portable system like the IBM 5100 was the IBM PALM processor, which implemented an emulator in microcode to allow e.g. running System/360 APL code on a 5100, as well as BASIC.
Despite [Bradford]’s claim that the 5100 was not a commercial success, it’s important to remember the target market. With a price tag of tens of thousands of (inflation-adjusted 2023) dollars, it bridged the gap between a multi-user mainframe with APL and far less capable single-user systems that generally only managed BASIC. This is reflected in that the Commodore SuperPET supported APL, and the 5100 was followed by the 5110 and 5120 systems, and that today you can download GNU APL which implements the ISO/IEC 13751:2001 (APL2) standard.
An audio distortion analyzer is a specialist piece of analogue test equipment that usually costs a lot of money and can be hard to track down on the second hand market. Finding one is a moment of luck for the average engineer then, but [Thomas Scherrer OZ2CPU]’s discovery isn’t quite what he might have hoped for. Nonetheless, his Bang and Olufsen K3 Distortion meter DM1 from 1979 is still an interesting and high quality piece of test equipment, and the video below the break makes for a worthwhile watch.
Bang and Olufsen are best known for high-end design Hi-Fi units, thus it’s a surprise to find that in the past they also manufactured test equipment. This distortion meter isn’t a general purpose one, instead it’s designed to measure tape recorders in particular, and it uses an elegant technique. Instead of injecting a sine wave and removing it from what comes out in order to measure the products of the distortion, it records a 333 Hz sine wave onto a tape, then measures the strength of its 3rd harmonic at 1 kHz as an indication of distortion. It’s a working distortion meter made with clever analogue circuitry for a fraction of the cost of the more conventional models that HP would have sold you at the same time, even if it doesn’t give the same THD figure you might have been looking for.
