Falk Joensson's
Learning Programming with Eas
(Easy Application Script Tutorial)

How the Computer Works:03. I/O Devices

Input devices such as the keyboard, the mouse, a microphone or webcam set and clear bits in the computer. When you press a key on the keyboard, its bit is set, and when you release it, its bit is cleared — however not in your computer, but in the keyboard's microcontroller. Microcontrollers are the simpler cousins (smaller, slower, cheaper) of the computer, but in principle, they work in the same way. In input devides, they are used to format the input information so that it can be transmitted efficiently to the computer. Without a keyboard microcontroller, you would need one cable line for every individual key each. Instead, the microcontroller sends the information about key state changes (pressed, held, released) as a sequential signal to the computer, using up only very few cable lines. There is a program built into the device microcontroller for doing that, and your computer has a compatible program, the driver, to decode the information from the device. Output devices such as the TFT monitor, the soundcard and the printer read bits from the computer, often also by help of further microcontrollers. Memory devices such as hard disk drives, CD/DVD drives and so on combine input and output technologies, often even when they are read-only: The mechanical drives (HDD, CD/DVD) are steered by PC output signals to read data on a PC input channel.
03. I/O Devices
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