At the most basic level, all PCs operate using a combination of input and output. Input refers to information provided to the PC, which could be characters you type on your keyboard, mouse actions such as clicks and right-clicks, and touchscreen gestures such as taps and swipes. Output refers to data generated by the PC that appears on your monitor (or perhaps on your printer). And you know from Chapter 1, “Getting to Know the PC,” that inside your PC the CPU is processing data, the hard drive is storing data, the memory is enabling data to be worked with, and so on. In other words, there’s a lot going on both inside and outside your PC, so who or what is making sure it all happens smoothly and accurately?