So what is the difference between a calculator and a computer? The fundamental difference is that a computer can be programmed in a way that allows the program to take different branches according to intermediate results, while calculators are pre-designed with specific functions built in. The distinction is not clear-cut: some devices classed as programmable calculators, sometimes with support for programming languages. Calculators also have the ability to store numbers into computer memory. Basic types of this store only one number at a time; more specific types are able to store many numbers represented in variables.

In general, a basic calculator consists of the following components:
1. Power source: batteries, solar cells or mains electricity (for old models), turning on with a switch or button. Some models even have no turn-off button but they provide some way to put off (for example, leaving no operation for a moment, covering solar cell exposure, or closing their lid).
2. Keypad (input device): consists of keys used to input numbers and function commands (addition, multiplication, square-root, etc.)
3. Display output: usually have liquid-crystal displays (LCD) as output in place of historical light-emitting diode (LED) displays and vacuum fluorescent displays (VFD).
4. Processor chip (microprocessor or central processing unit): Scanning (Polling) unit, Encoder unit, X register and Y register, Flag register, Permanent memory (ROM), User memory (RAM), Arithmetic logic unit (ALU), Binary decoder unit. A clock rate of a processor chip refers to the frequency at which the central processing unit (CPU) is running. It is used as an indicator of the processor’s speed and is measured in clock cycles per second or the SI unit hertz (Hz). For basic calculators, the speed can vary from a few hundred hertz to the kilohertz range.