Real Time versions in Linux

Standard Linux can be used for Soft Real-time applications where the sample time is relatively long,say tens of milliseconds which missed timing schedules the application could tolerate.
Hard Real-time applications require rigid determinism and fast timing. Real-time variants of Linux are suitable for such applications. Real-time versions of Linux offer important advantages to control Engineers in providing an open source operating system that rivals the performance of the proprietary Real-time kernels.
Linux offers two flavors to implement Real-time tasks,

• RealTime Linux(RTLinux)
• RealTime Application Interface(RTAI)

To implement Hard Real-time tasks, not like standard Linux kernel, here we need special methods to handle interrupts and timing performance. I feel RTAI is easier to install and configure than RTLinux. You could find the better and the easiest guide to install and configure the RTAI with the standard Linux kernel here.