The parts of a computer

Hardware is the machine; software is the instructions that run it. There are two main kinds. The operating system manages the computer: it keeps the files, shares memory between programs, controls the devices, and starts and stops programs. A desktop computer and a phone each have an operating system of their own kind. Application software does a task for the user, such as writing a text, drawing or playing a game. A device driver is a small program that teaches the operating system how to use one device, such as a printer; a new device may need its driver. A program is stored as a list of instructions. To run it, the processor repeats three steps for each instruction: it fetches the instruction from main memory, decodes it (works out what it asks) and executes it. Then it moves to the next instruction. This cycle repeats billions of times a second in a real processor, but each step is small.