dedicated rtos and coexist kernel realtimelinux

[Handy Madinata <handy@thunderbolt.ee.itb.ac.id>]

hi all, forgive me for my stupid questions..

does anyone can mention some items that differ an rt system that built
together with a general-purpose host OS (like rtlinux, rtai) with a
dedicated rtos (like qnx, vxworks, spring, maruti, yartos), in case that
now:

- some dedicated rtos can implement a posix compliant environment and they
built their own services (file system, networking, gui) from scratch

- some of them also used microkernel approach that separate
interupt-processing, scheduling, and message-passing development from
other services

more of them, they used 'the safe' MMU memory-protecting mechanism that
can't be found at rtlinux or rtai realtime module-task

and also, I've heard that qnx services except of the microkernel is stayed
at user-space (user-level file-system, drivers) , how could they do that..

thanks beforeward for your kindness..

-=/Handy Madinata\=-