It accepts the instructions and data input by users, and generates or stores them into useful information after being processed by the mathematics and logic unit of the central processor. Personal computers, tablets, iPad, mobile phones and other common calculators. Input unit: keyboard, mouse, scanner, touch screen, etc. Host part: it is a system unit, protected by the host shell, including a bunch of boards, CPU, main memory and so on. Output unit: screen, printer, etc.