An analog computer is also called a
continuous computer because 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.