What a computer system is

A computer is an electronic device that can be programmed to accept data (input), process it, and produce a result (output). Think of uploading an ordinary photo to an app that turns it into a cartoon: the photo is the input, the app processes it, and the cartoon is the output. A computer together with its hardware and software is a computer system.

The central processing unit (CPU) is the brain of the computer. It is built on integrated circuits (chips). It fetches programs and data from memory, processes them, and stores the results back. Inside the CPU are registers: tiny, very fast memory locations that hold data and instructions for a moment while they are being used.

The CPU has two main parts:

• The Arithmetic Logic Unit (ALU) does all the arithmetic (adding, subtracting…) and logic (comparing: is A greater than B?) operations.
• The Control Unit (CU) interprets instructions, controls the order in which they are carried out, and guides the flow of data between the parts of the computer.

Input devices send data and control signals into the computer, converting them into digital form: keyboard, mouse, scanner, touch screen, microphone (voice input), and a braille keyboard for people who cannot see. Input data is held first in RAM; to keep it permanently, it is saved to secondary memory.

Output devices convert digital information back into a form people can understand: monitor, projector, speaker, headphones, printer, and a braille display. Printers can be inkjet, laserjet or dot matrix. A 3D printer goes further: it builds a solid, physical object from a digital design, layer by layer.