Analog computers are a largely obsolete technology today, but they were critical computing devices before the rise of digital computers. By using continuously changing electrical, mechanical, or hydraulic quantities, analog computers were able to model complex situations and provide solutions without needing programming. Let‘s explore what analog computing is, its history, how these machines worked, examples still used today, and why they eventually faded from prominence.
A Brief History of Analog Computers
While analog computing technology has existed in various forms for centuries, the first recognizable modern analog computers emerged in the late 19th and early 20th centuries from inventors and engineers tackling complex mathematical problems.
One of the earliest prototypes was conceived in the 1890s by Serbian mathematician Mihailo Petrović Alas, who designed a hydraulic analog computer to solve differential equations. This was followed in 1898 by the harmonic analyzer invented by A.A. Michelson and S.W. Stratton, which could combine mechanical motions to produce varying waveforms.
However, one of the major breakthroughs came in 1931 when American electrical engineer Vannevar Bush created the differential analyzer. Using integrators made of variable-speed gears, Bush‘s machine could rapidly solve differential equations needed for tasks like modeling transmission lines – a major innovation at the time.
During World War II, analog fire control computers were essential for aiming guns and calculating artillery trajectories. Large, complex analog computers were built to simulate flight dynamics and aid other military efforts. Analog computing power underpinned pioneering technologies like synthetic aperture radar as late as the 1980s.
How Analog Computers Work
Unlike digital computers which manipulate discrete values represented by numbers or codes, analog computers work by measuring continuously changing physical quantities. This could involve electrical signals, fluid pressures, mechanical motions of gears or levers, or other analog means.
The analog computer is composed of different modules, each able to perform an operation like addition, integration, multiplication, or generation of special functions. By interconnecting inputs and outputs between many such modules, complex problems can be solved. For example, systems of differential equations important for modeling dynamic systems can be analyzed by using voltages to represent quantities of interest, then scaling, feeding back, and integrating these signals as needed.
Because they leverage directly measurable physical phenomena instead of step-by-step programs, good analog computers can solve some problems much faster than early digital computers, despite their imprecision. However, as digital technology rapidly improved, analog computers became obsolete for most applications by the 1960s and 70s.
Examples of Analog Computers
Though no longer used for major computations, analog computers actually still abound in numerous real-world tools:
Thermometer
A thermometer computes temperature using the analog expansion of mercury. As temperature rises, the mercury expands higher up the graduated glass tube of the thermometer.
Speedometer
A speedometer measures a vehicle‘s speed using rotating magnets and metal cups connected by springs to register speed mechanically and drive an indicator needle.
Analog Clock
Quartz crystal vibrations driven by a battery generate steady analog pulses to tick the seconds of an analog clock.
Seismometer
A seismometer uses a suspended mass and recording apparatus to translate ground movements into measurements of earthquake severity.
Voltmeter
An analog voltmeter uses a rotating coil and needle to measure and display voltage differences on a scale proportional to voltage.
While these common analog devices persist, more complex analog computing machines have been entirely superseded in scientific and industrial applications by precise, programmable digital computers in the modern era. However, their influence on computing history is undeniable.
