The computer system

A computer is an electronic device that can be programmed to accept data (input), process it and generate results (output). A computer together with its extra hardware and software is a computer system. Its main parts, the CPU, memory, input/output devices and storage devices, work together as one unit. Computer systems range from high-end servers to desktops, laptops, tablets and smartphones.

Central Processing Unit (CPU), the brain of the computer (also called the processor or microprocessor):

• It sits on one or more microchips called integrated circuits (ICs), made of semiconductor materials.
• It fetches the program and data from memory, performs arithmetic and logical operations as instructed, and stores the result back in memory.
• While working, it keeps data and instructions in small, fast local memories called registers.
• Arithmetic Logic Unit (ALU): does all arithmetic and logic operations.
• Control Unit (CU): controls the order in which instructions run, interprets them, and guides the flow of data between memory, the ALU and input/output devices.

Input devices send data and control signals to the computer, converting input into digital form: keyboard, mouse, scanner, touch screen; braille keyboards for visually impaired users; and voice input (as in voice search). Input data is first held in the main memory (RAM); for permanent storage, data and instructions go to secondary memory.

Output devices turn digital information into a form people understand: monitor, projector, headphones, speakers, printer; a braille display for visually impaired users.

• A printer gives hardcopy output; common types are inkjet, laserjet and dot matrix.
• A 3D-printer builds a physical object from a digital 3D design; it is used to make prototypes in industry and is being explored in medicine, even for body organs.

Example (new): when you speak a question to a phone assistant, the microphone is the input device, the processor works out the answer from data in memory, and the speaker reading the answer aloud is the output device.