> What is the significant difference between ordinay Linux (Slackware, Redhat and other commercial brand..) and a real time version ?< The Linux kernel is a POSIX (regular) multitasking kernel. It tries to optimise the scheduling in such a way as to get as high a throughput (of processes) as possible. The problem is that this is not conducive to a real time system where accurate time is critical (there is no direct assessment of timing). RTLinux implements a new kernel with the needed scheduling algorithms (for real time system), among other things. The normal Linux kernel then sits on top of RTLinux as a minor process; your Linux distribution (Debian, RH, ...) will then work as normal. The advantage of this is that the RTLinux dev team can write a simpler kernel, and concentrate on the important real time stuff.