Operating System (OS)

When you turn on your smartphone, a lot of parts and apps start moving busily behind the screen. The YouTube app wants to show video on the screen and play sound through the speaker. The messaging app waits for an internet connection so notifications arrive on time. If the apps fought over the hardware and grabbed whatever they wanted, your phone would freeze in no time.

The OS is the one that directs this traffic. Like a hotel's general manager, it carefully decides how much of the central processing unit (CPU) each app gets and which room in the main memory (RAM) it stays in. It keeps guest apps from touching the machine's circuits directly, and it shares resources fairly.

Thanks to this, app developers don't have to study the complicated inner workings of the hardware. If they build an app to the standard rules the OS provides, it will generally run as-is on many devices that use the same OS.

When you click a mouse or tap the screen with your finger, countless electrical signals turn into 0s and 1s and flow through the machine. But you never have to understand those binary signals yourself. The OS turns them into friendly icons and windows, acting as an interpreter between people and computers.

The OS also works as a reliable security guard. Even if one app crashes and is forced to close, other apps and the whole phone won't freeze, because the OS walls off each app's workspace from the others.

If a suspicious piece of malware tries to secretly peek at your private data or delete system files, the OS can block its access right away. Keeping every program inside a safe, defined fence like this is the OS's important security job.

To be a little more precise, deep inside every OS sits a core management program called the kernel. The kernel is the heart of the OS. From the moment the computer turns on until it shuts down, it stays in memory and keeps watch over all of the device's hardware resources.

The kernel is also why you can listen to music, browse the web, and send a message all at once. A single CPU core can only handle one task at a time. Modern CPUs have several cores, so they can truly do that many things at once. But there are far more running apps than cores, so the kernel slices time into tiny pieces and hands them out in turns. This is called time-sharing multitasking.

The OS switches between tasks hundreds or even thousands of times per second. To the human eye, it looks as if many apps are running at exactly the same time. Windows, macOS, Android, iOS, and Linux all look different on the surface, but each one is an OS that runs its hardware by this same core principle.