History of the calculator: the microchip age and virtual age

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The history of the calculator is split into two pages and has four main chapters, listed below. If you want to read part 1 of the article, please go here.

  1. Beginnings: The Mechanical Age
  2. Business Calculator: The Electronic Age
  3. Pocket Calculator: The Microchip Age
  4. Calculators Now: The Virtual Age

Pocket Calculator: The Microchip Age

It had taken 3,700 years to move from the abacus to the first mechanical calculators and a further 250 years for mechanics to give way to electronics. Yet it would take barely a decade for the calculator to make its third metamorphosis, from a heavy, bulky, expensive desktop machine that needed AC mains power to a cheap and compact battery or solar-powered device that would slip into a pocket or wallet.

To make that transition, engineers had to solve three huge principal challenges: replacing boards of transistors with integrated microchips, designing less power-hungry electronics and displays that could run on batteries and developing slimmer, simpler control mechanisms.

Texas Instruments prototype ‘Cal-Tech’ prototype of 1967 with its compact form was a prophet of the future, but it still used transistors and needed mains power.

Semiconductor revolution

However, within the next thee years, calculator development became the leading edge of Large Scale Integration (LSI) semiconductor development, with strategic alliances formed between the mostly Japanese calculator manufacturers and the largely U.S. semiconductor companies. Thus Canon teamed with Texas Instruments, Hayakawa Electric (Sharp Corporation) with North-American Rockwell, Busicom with Mostek and Intel, and General Instrument with Sanyo.

The Sharp QT-8B
Sharp QT-8B: Microchip and battery powered. Photo: Vintage Calculators

By 1969, a calculator could be made using just a few low power consumption chips, allowing the size and power consumption to be drastically reduced. The first of these appeared from Japan: Sharp’s QT-8D Micro Compet. This used four Rockwell chips each equivalent to 900 transistors; one to power the green fluorescent display, the second to control decimal point, the third to handle digital addition and register input control and the fourth to process arithmetic and provide registers.

By modern standards this seems impossibly primitive, yet this Sharp calculator represented a great leap forward, especially when they produced an alternative model, the QT-8B that replaced the AC power supply circuitry with rechargeable cells, allowing it to be battery powered and completely portable.

Within a year, the market in ‘handheld’ calculators had started to take off with machines like the Sharp EL-8, Canon Pocketronic and Sanyo ICC-0081 Mini Calculator all selling briskly, despite costing the equivalent of more than $2,000 in today’s money.

Pocket calculator

The Busicom LE-120 Handy
Busicom LE-120 Handy: first pocket calculator. Photo credit: Dentaku Museum

Yet even as they were introduced, these calculators were already obsolete. In that same year, 1970, the Japanese company Busicom released their Junior desktop model that boasted the first ‘calculator on a chip’ - the Mostek MK6010 that combined all four functions plus decimal point and display on one 4.6mm-square chip.

Within months, Busicom had used the same technology to produce the LE-120 ‘Handy’ - a much smaller machine, sporting an LED (Light Emitting Diode) display, and running on four AA batteries. The pocket calculator had arrived.

The 1973 Sinclair Executive
1973 Sinclair Executive: calculator as desirable object

Busicom also followed an interesting ‘blind alley’ at this time by developing a series of desktop calculators powered by the first Intel chip set arrayed around the pioneering 4004 microprocessor.

It proved overkill for the calculator so Busicom freed Intel to sell the chip-set elsewhere. As the 8000 series, it went on to drive the first generation of PCs.

The Busicom LE-120 pocket calculator was followed in late 1971 by the American-made Bowmar 901B (‘The Bowmar Brain’), still a fairly chunky 1.5 inches thick, and in mid-1972 from Britain by the first ‘slimline’ calculator, Clive Sinclair’s elegant £99 ($200) Executive, less than a centimeter thick and weighing only 70 grams.

The main problem with these pioneering machines was that they were too expensive for most consumers (multiply prices by three to see current values).

They were also still limited to basic arithmetical functions and their LED displays drained the batteries very quickly.

Cheaper, Better Calculators

Within a year, Sinclair had produced the Cambridge as the first low-cost calculator, priced at £29.95 (or £24.95 in kit form). The Sinclair calculators cost far less than the competition, but had an ugly bulge in the back for the PP9v battery and with a design that frequently led to errors when doing compound sums.

The Hewlett HP-35
Hewlett HP-35: first scientific calculator

Meanwhile Hewlett Packard (HP) had been developing a ‘scientific’ calculator. Launched in early 1972, the $395 HP-35 was an almost pocket-sized calculator with trigonometric and algebraic functions.

Within a few months, Texas had hit back with their own SR-10 algebraic entry pocket calculator using scientific notation for $150. The SR-11 featured an additional key for entering Pi, followed in 1974 by the SR-50 which added log and trig functions to compete with the HP-35 and in 1977 the mass-marketed TI-30 line. Slide rule sales started to plummet.

By this time, calculators had also started to become ‘programmable’ - accepting special inputted instructions.

Again, Hewlett-Packard led the way with their HP-65 of 1974 that had a capacity of 100 instructions, and could store and retrieve programs with a built-in magnetic card reader that also formed the label to show the new assigned functions of the transferrable F-keys.

The Hewlett HP-65
HP-65 Programmable: buying a calculator could be a Big Deal.

By 1979, HP were making an alphanumeric programmable calculator, the HP-41C, that could be expanded with RAM memory and ROM software modules, as well as peripherals like bar code readers, micro-cassette and floppy disk drives, paper-roll thermal printers, and miscellaneous communication interfaces, like RS-232.

The Soviets also produced an interesting range of Elektronika programmable calculators in the late 1970s. People managed to produce hundreds of programs for these machines, from practical scientific and business software to fun games for children. The Elektronika MK-52 calculator, featuring internal EEPROM memory for storing programs, was even used in the Soyuz spacecraft as a backup flight computer.

Subversive ‘hacker cultures’ grew up, dedicated to mining the undocumented “hidden’ capabilities from the Elektronikas and the HP-41.

Calculator wars

The Texas TI 2550
Texas Instruments TI-2550: a calculator for just $9.95. Photo credit: Curtis Perry

Meanwhile, back in the mainstream, the struggle continued to make pocket calculators more functional and affordable. The early calculators were very expensive luxury items because they used specialised mechanical and electronic components produced in limited runs.

As the market developed, the components became commoditised and prices dropped. By 1974, the bulky TI 2550 appeared as the first sub-10 dollar calculator and within a further two years, the price of the basic 4-function pocket calculator was about a twentieth what it had been five years earlier.

Good news for consumers, bad news for manufacturers whose high margins had disappeared. During the ‘Calculator Wars’ of the mid-1970s, most of the specialist and ‘me, too’ manufacturers disappeared, leaving a market dominated by five major brands: Sharp, Texas, HP, Canon and the new kid on the block, Casio.

The display was now the key technological challenge – replacing LEDs with something less power-hungry. The Liquid Crystal Display (LCD) seemed to be the obvious answer but the early LCDs were flaky and required a filament lamp for illumination, using almost as much power as LEDs. A clutch of Rockwell-sourced models were manufactured during the early 1970s under such brands as Dataking, Harden, Ibico, Lloyds and Rapid Data Rapidman, but none lasted more than a year or two.

Sharp’s "COS" (Calculator On Substrate) LCD technology was better but too expensive.

By the mid-1970s, calculators were starting to use twisted nematic black on grey crystal displays, with yellow filters used at first to protect against UV.

The Teal Photon
Teal Photon: solar pioneer. Photo: Vintage Calculators

These could be driven directly by the IC chip. At the same time, improvements to the electronics inside the calculators, using single chips and CMOS logic cells, again pioneered by Sharp in its EL-801, meant that transistors only drew power when they changed state.

The end result, by 1978, was a new generation of pocket calculators with power consumption so low that they could be driven by solar cells.

The first of these, the Sharp EL-8026, and Teal Photon, along with the credit card-sized Casio LC-78 brought the calculator close to its ultimate form as the 1970s ended.

On the next page we look at the virtual age of the calculator and how calculators look set to develop in the future.

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Last update: 24 March 2014

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