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Vintage Electronic Calculators

The dawn period for electronic calculators begins in the early 1960s and ends in the early 1970s. Mechanical calculators had reached a remarkable level of sophistication by the early 1960s, some could even extract square roots, but all were large, heavy, expensive and required precision care and maintenance. These machines were widely used but were largely out of the reach of modest organisations and individuals.

Two lines of development matured and converged in the early 1960s, setting the stage for the dawn of personal electronic calculators.

The first development was the progress of digital computer technology from its infancy in the 1940s to a confident adolescence at the end of the 1950s. Techniques for electronic logic, calculation and memory had matured and engineers familiar with these techniques were seeking new applications. It is interesting that many of the original ground-breaking electronic calculators were not produced in the R&D divisions of established calculator and computer companies but by individuals or small teams working in start-up environments.

The second development was the progress of the transistor from laboratory experiment to cheap, reliable commercial product. Before transistors were readily available digital logic circuits were built with large, hot vacuum tubes. The resulting machines were large, power hungry and maintenance-intensive, limiting their use to well-funded organisations. The arrival of reliable inexpensive transistors at the start of the 1960’s allowed creative engineers to apply transistor digital logic to the production of better and smaller calculating machines.

The names of these first visionary engineers are little known but they and their first machines should be better recognised:

These machines were the start of a revolution that put unprecedented levels of calculating power into the hands of individuals. People were now able to focus on ideas and development, rather than becoming bogged down in the mechanics of calculation.

The dawn period for calculators is defined here as the period when the machines were constructed with individual diodes, transistors and (later) basic integrated circuits. First-generation diode-transistor machines typically had around 500 transistors and 1500 diodes. Circuits were complex but can be fully deduced from an example machine, given enough time and care. Construction of these machines required skilled labour and was done with a high standard of workmanship. These machines display care in design and pride in the standard of construction. All of these factors tended to limit the number of manufacturers who were able to produce such machines and the dawn period sees a relatively small number of high-quality machines and manufacturers.

The dawn period for calculators was brought to an end by the development of integrated circuits. Integrated circuits allowed many transistors to be placed on a silicon chip, producing a small, reliable and ever-cheaper functional block. Small-Scale Integration (SSI) developed slowly through the 1960s and was used in second-generation machines of the late-dawn era, enabling them to become more sophisticated but also smaller and simpler. The electronic functions of SSI chips were basic and the fundamental design of such machines remains available by analysis of an example machine. Design and construction quality remained high.

Medium-Scale Integration (MSI) became possible in the late 1960s and allowed increasing numbers of functional units to be placed on a chip. By the end of the 1960s third-generation machines began to appear where six, five or even fewer chips could hold the logic of the entire calculator. The design and construction effort shifted from machine building to chip design and manufacture. As the chip companies became the centres for design innovation and manufacturing skill, design information was increasingly hidden inside their chips. Calculators became smaller and more sophisticated, and their physical construction became an ever-simpler assembly of ever-fewer parts. These parts were increasingly complex “black boxes” whose internal design was hidden and unknown, meaning that even if the external circuit of such a calculator was fully traced, it would simply show connections between unknown black boxes. Such a circuit tracing gives little information about how the calculator actually works.

The dawn era of electronic calculators was ended by Large-Scale Integration (LSI), which became viable at the end of the 1960s. In LSI calculators the entire circuit was contained in one chip. All of the complexity was now purchased from the chip manufacturer and as chip manufacturing volumes grew, prices fell. Almost any electrical manufacturer could buy LSI chips and assemble calculators. Calculator companies sprang up like mushrooms in the early 1970s and relentless competition drove prices into a steep downwards spiral. By the late 1970s calculators had become ubiquitous and cheap, they were constructed and used like commodities and it was not economic to diagnose or repair them. In any case, electronic calculator design was no longer comprehensible to anyone except the chip designers.

The dawn was over by the middle 1970s. Technology had progressed rapidly over a little more than ten years, electronic calculators that were high-priced, craftsman-built and cutting edge had become inexpensive, mass-produced and mainstream.