Once a mission critical software system has been developed, verified, and fielded; developers, managers and customers typically enter a paranoid state where changes to the system are fiercely resisted. Why? Often it’s because in anything but a trivial software system, opening up the code to remove a defect or add a feature invariably opens the entire software system to suffering a fresh round of new, yet to be discovered, defects. In other words, in this craft we call “software engineering,” making changes can all too often mean inserting bugs. One way to break this change paralysis is to use technology that isolates the change to the defect prone or feature deficient area, while leaving other areas identical to the day they were tested and accepted. Deos™, a time and space partitioned RTOS, certified to DO-178B, level A since 1998, includes such technologies and thus allows mission critical systems to evolve and innovate at a faster rate and lower cost. This paper describes some of those key Deos technologies.