Electronic calculators are the modern counterparts of the adding machine but are able to perform many more functions.
Calculators are a direct outgrowth of digital technology. In some calculators commands are permanently built into the system. The commands are programmed, that is planned so that one command follow another, in groups called microprogrammed routines. Such programming provide a way of drastically reducing the cost of the integrated circuit that constitute a calculator's many circuitry. The programs, however, cannot be changed by an operator.
By contrast, in calculators that can be programmed by an operator, some or all the stored commands can be changed. Thus a so-called programmable calculator is actually a simple micro-computer, one that is programmed from a special keyboard rather than by using a symbolic computer language.
In a hand held programmable calculator, the principle of programmed calculator, the principles of programmed systems are applied in a way similar to that of a computer. Four main functions are involved; input, storage, processing, and output, input involves taking information from switches operated by the keyboard, and translating it into digital code. Storage, or memory, involve holding information based on the old, and output is the display of this information by means of light emitting diodes. The magnetic card system used in such calculators corresponds to a computer's magnetic tape unit, but it can store only instructions, not numbers.
The memory consists of four different units, the program memory, the microprogram memory, the so-called constant memory, and the number memory. The processing parts consists of two sections; the controller and the arithmatic and logic unit (ALU).