# Calculator - Internal Working

Internal Working

In general, a basic electronic calculator consists of the following components:

• Power source (battery or solar cell)
• Keypad - consists of keys used to input numbers and function commands (addition, multiplication, square-root, etc.)
• Processor chip (microprocessor) contains:
• Scanning unit - when a calculator is powered on, it scans the keypad waiting to pick up an electrical signal when a key is pressed.
• Encoder unit - converts the numbers and functions into binary code.
• X register and Y register - They are number stores where numbers are stored temporarily while doing calculations. All numbers go into the X register first. The number in the X register is shown on the display.
• Flag register - The function for the calculation is stored here until the calculator needs it.
• Permanent memory (ROM)- The instructions for in-built functions (arithmetic operations, square roots, percentages, trigonometry etc.) are stored here in binary form. These instructions are "programs" stored permanently and cannot be erased.
• User memory (RAM) - The store where numbers can be stored by the user. User memory contents can be changed or erased by the user.
• Arithmetic logic unit (ALU) - The ALU executes all arithmetic and logic instructions, and provides the results in binary coded form.
• Decoder unit - converts binary code into "decimal" numbers which can be displayed on the display unit.
• Display panel - displays input numbers, commands and results. Seven stripes (segments) are used to represent each digit in a basic calculator.

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