Operating System Design/Case Studies/QNX
The QNX Operating System is ideal for realtime applications. It provides multitasking, priority-driven preemptive scheduling, and fast context switching ‒ all essential ingredients of a realtime system.
QNX is also remarkably flexible. Developers can easily customize the operating system to meet the needs of their application. From a "bare-bones" configuration of a kernel with a few small modules to a full-blown network-wide system equipped to serve hundreds of users, QNX lets you set up your system to use only those resources you require to tackle the job at hand.
QNX achieves its unique degree of efficiency, modularity, and simplicity through two fundamental principles:
- microkernel architecture
- message-based interprocess communication
QNX's microkernel architecture
QNX consists of a small kernel in charge of a group of cooperating processes. The structure is more like a team than a hierarchy, as several players of equal rank interact with each other and with their "quarterback" kernel.
The QNX Microkernel coordinating the system managers.
The kernel is the heart of any operating system. In some systems the "kernel" comprises so many functions, that for all intents and purposes it is the entire operating system! But the QNX Microkernel is truly a kernel. First of all, like the kernel of a realtime executive, the QNX Microkernel is very small. Secondly, it's dedicated to only two essential functions:
- Message passing
- the Microkernel handles the routing of all messages among all processes throughout the entire system
- the scheduler is a part of the Microkernel and is invoked whenever a process changes state as the result of a message or interrupt
Unlike processes, the Microkernel itself is never scheduled for execution. It is entered only as the direct result of kernel calls, either from a process or from a hardware interrupt.