My desktop computer uses an operating system (OS) – Linux, of course – but "operating system" is a very loose term, often describing everything that makes a computer work, from launching programs, communicating over a network, managing filesystems, and presenting the user with a sophisticated graphical user interface. Much of this functionality lies outside of the kernel of the OS, and many computers are used in such a way that they don't need some of these facilities: specifically, servers that generally run headless with administrative and user access performed over some form of network.

In the world of embedded computers, a real-time operating system (RTOS) is much more focused on being a kernel. The simplest microcontroller might require no OS at all, which is known as bare metal programming. Many microcontroller applications are written in this way, and with the judicious use of timers and interrupts, a version of multitasking can be obtained. At some point, however, this cooperative multitasking can lead to spaghetti code that is difficult to understand, debug, and maintain.

Somewhere in the spectrum of applications, from a humble microcontroller sensing when to pop the toast out of your toaster to a complex navigation and control system for a robot, a point is reached wherein some sort of operating system is desirable or even necessary. This type of operating system, RTOS, does not at first glance bear too much resemblance to a server or desktop OS.

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