RTLinux Internal Architecture :

RTOS comprises only a Kernel. For a complex embedded system, an RTOS can be combination of various modules, including the Kernel, networking protocol stacks, and other components.Standard time sharing OS and hard real time executive running on same machine. Kernel provided with the emulation of Interrupt control H/W. RT tasks run at kernel privilege level to provide direct H/W access. Rt linux runs Linux kernel for booting , device drivers ,networking, FS, process control and loadable kernel modules. Linux kernel runs as a low priority task on the RT kernel hence making sure it cannot preempt any RT task.

The RT kernel is actually patched over the Linux kernel and then recompiled to work as rtlinux system.The real-time operating system, another key component of a data-acquisition system is the device driver that controls the digitizing hardware.RT tasks cannot use Linux system calls , directly call routines or access ordinary data structures in Linux Kernel.There are two ways to install a real-time Linux system. First, you can purchase a pre-configured embedded Linux distribution,RT task allocated fixed memory for data and code Therefore RT Processes without memory location features. 

     VM layer only emulates the Interrupt Control.The 0 level OS does not provide any basic services that can be provided by Linux i.e only RT services, No primitives for process creation, switching or MM.Uses software stack for switching and not the expensive H/W switching. RT kernel is not preemptable