One of the most significant developments of computer architecture was the discovery that binary numbers were the least expensive form for electronic storage.
Two different approaches to registers have been pursued.
The first was to have an electronically-controlled switch for each possible state of each digit of the register. Any one switch, when on, turns off all the other switches. This system is stable, and is standard engineering practice.
The other method is to map several states to the charge in one capacitor. This approach can sometimes be used to save money. For example, most digital cameras use a charge coupled device as their sensor.
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