What is an operating system
You listen to music while searching the web, and messages keep arriving in the meantime. How does one computer do so many things at once? Because there's an invisible caretaker behind the screen.
All we see are apps
When you turn on a computer, what you see are apps like messages, music, and a browser.
But underneath them, something you can't see is always at work.
Let's lift up the screen and take a look.
Lift the screen and see what was hiding underneath.
The thing holding up all the apps is the operating system, or OS for short.
Windows, Android, iOS: you've probably heard these names, and they're all operating systems.
It sits between apps and hardware
The operating system sits right in the middle.
Above it are the apps we use, and below it is the hardware we saw earlier: parts like the CPU and memory.
The operating system sits between the two and connects them.
The operating system sits on the middle layer, between the apps and the hardware.
Apps don't touch the parts directly. Instead, they ask the operating system: "Give me some memory," "Open this file, please."
The operating system takes those requests and handles them.
Looking after many apps at once
A computer always has several apps running at the same time. Music has to play sound, the browser has to draw the screen, and messages have to pop up notifications.
The operating system takes all these requests at once and handles them in turn.
The apps' requests gather at the operating system, which handles them one by one.
To us, everything seems to happen at once, but in fact the operating system is switching between apps very quickly.
We'll see the secret behind this in detail a little later, in the time-sharing lesson.
Refereeing shared parts
There's only one of each part, but many apps want to use it. There's only one speaker, for example.
When music and a notification both try to make sound at the same time, the operating system steps in.
It's the referee that decides who uses what, and when.
Music and a notification share the single speaker.
What if there were no referee? Two apps would try to grab the same part at once, clash, and freeze.
Because the operating system keeps order, we can use many apps without worry.
What if there were no operating system?
The best way to feel what the operating system does is to imagine it isn't there.
Flip the toggle below, and you'll see at a glance how different things are with and without it.
Flip the toggle to compare having an operating system with not having one.
With an operating system, apps run along nicely together; without one, they crash into each other and everything falls apart.
Thanks to this invisible caretaker, we can use computers comfortably without knowing all the complicated details.