What is the difference between analog computers - digital computers - and hybrid computers - give examples of each type?

Answer 1

Analog computers are also called continuous computers, as there are no discontinuities in their computations. A mechanical analog computer might represent variables by rotation rate of shafts, any given shaft can rotate at any speed and will smoothly accelerate or decelerate its rotation as the calculation proceeds. An electronic analog computer might represent variables by voltages, say any voltage between -20VDC and +20VDC with voltages smoothly varying as the calculation proceeds.

• Bush differential analyzer at MIT, electromechanical, 1929.
• Norden bombsight, electromechanical, 1930s through 1960s (used in WW2, Korea, and Vietnam!).
• Various commercial electronic differential analyzers sold from 1950s through 1970s, electronic.
• Murray/Walker simultaneous equation solver, electronic, 1949.
• Vacuum operated cruise control in cars, mechanical/pneumatic.
• Resistor/capacitor 3D mesh water table models, electronic.
• etc.

Digital computers on the other hand have discontinuous states that they jump from one to another.

• ABC: Atanasoff-Berry Computer, simultaneous equation solver, 1942
• ENIAC, late 1945
• UNIVAC I
• IBM 700 and 7000 series
• DEC VAX
• Desktops and laptops
• Both of the computers in your cellphone
• etc.

Hybrid computers are simply computer systems that combine both analog and digital computers together. Usually the digital computer controls the analog computer, reconfiguring it and entering new data each time the analog computer completes one problem, to have it solve a different one.

• Most were custom "one off" systems built by individual labs or universities by buying a standard COTS digital computer and a standard COTS electronic analog computer, and customizing them to work together as needed.
• One example of such a machine used a DEC minicomputer and an analog computer to model heat flow from a nuclear reactor fuel rod to circulating coolant. The analog computer was programmed on its plugboard to do a rapid solution through a single radial slice of the system, the digital computer was programmed to enter new parameters into the analog computer for each slice starting at the coolant entrance end of the fuel rod and collect and record the results of each slice. The machine could solve the problem to adequate accuracy much faster and more cheaply than an all digital system or all analog system of the time period.

Answer 2

An analog computer is also called a continuous computerbecause its variables change smoothly and continuously during operation, with no jumps or discontinuities. Some examples: a mechanical analog computer might represent variables as speed of rotation of shafts the rotation rates vary smoothly, an electronic analog computer might represent variables as voltages between -15V and +15V the voltages vary smoothly.

A digital computer represents its variables using codes or symbols that change in discrete values during operation.

Analog computers are usually harder to reprogram than digital computers as they typically have to effectively be taken apart and reassembled to solve a different problem.

A hybrid computer is any combination of analog and digital computers interconnected to solve a problem that would be too complex or expensive to solve entirely on an all analog or all digital computer. These machines are rarely seen now as digital computers have gained performance and dropped in cost. Specialized Digital Signal Processor (DSP) digital computers have effectively replaced the remaining uses of hybrid computers.

• Analog computers operate on continuous forms of data representation. (e.g. voltages, currents, speed of rotation, amount of sand accumulated in pile) They usually are only accurate to 2 or 3 digits.
• Digital computers operate on discrete forms of data representation. (e.g. numbers, character codes, 1s and 0s) They can be as accurate as you want.
• Hybrid computers operate on both forms of data representation.

Analog and Hybrid computers are rare these days.

A "hybrid" computer is a computer that does part of its calculation digitally and part in analog. They are very rare these days if they exist at all anymore. Nobody wants to design analog computing circuits. Few engineers are trained in analog computer design and usage, so it is not considered as an option.

I worked with a system that used a hybrid computer to draw high speed stroke graphics on a CRT. The digital part drew the high speed lines and conics, the analog part did translations, rotations, bordering, and muxing in raster sweeps from a separate sweep generator that used another analog computer to draw both rectangular and arc shaped rasters.