"They can save SWaP with fewer boxes on the airplane, but with all these different pieces of software on the same CPU, we have a potential conflict where one piece of software might have an error, whether inadvertently or maliciously, and impacts the operation of other software. That's where the time and space partitioning comes into play," King adds."Maybe this really critical piece of software went through a very rigorous development verification process that may take a lot of time and be very costly," King proposes, "and then I might have some non-critical piece of software that went through a much less rigorous process and it may have errors in it. Now I can safely mix them on the same CPU because the operating system, the RTOS underneath, guarantees with time and space partitioning that the lower-criticality piece of software that I have less confidence in cannot somehow affect the correct operation of the higher criticality piece of software."The latest RTOS technology from Green Hills Software in Santa Barbara, Calif., combines the benefits of partitioning and virtualization, and offers the ability to virtualize Microsoft Windows or Linux in safe and secure embedded systems. "Introducing Microsoft Windows or Linux, whose security is only certified to protect against casual and inadvertent attempts to breach the system security, into any mil-aero application is fraught with danger to both lives and national security," says Dan O'Dowd, chief executive officer of Green Hills Software."The only way these operating systems can be made safe and secure is to virtualize them in a 'padded cell’' whose safety and security is sufficient to protect classified and other high-valued information against sophisticated threat agents; i.e., SKPP EAL6+/High Robustness and RTCA DO-178B Level A," O'Dowd explains. "Our Padded Cell virtualization technology is the only virtualization technology to offer the RTCA DO-178B Level A and SKPP EAL6+/High Robustness necessary to prevent Windows and Linux from harming the security and safety of the system."PerformanceAlthough a feature-rich RTOS can be advantageous, "in general, it's wise to avoid overkill," Carbone says. "In other words, don't select an RTOS with more bells and whistles than you need; it just adds complexity, complicates learning and using, slows down development, and often costs more. Instead, identify the technology that’s appropriate for the task at hand.""You want an operating system imposing as little overhead of its own as possible," King says, "so that you leave as much CPU bandwidth as possible for the actual value-added software -- whether it’s a flight control system, ground proximity warning system, or whatever it might be. People are very sensitive to the performance of the operating system and there are wide differences in the commercial off-the-shelf (COTS) products out there in that regard."Consider how well the RTOS can respond to events, Day recommends. "Applications in the mil-aero industry often have to respond to many more events in a shorter time span than commercial systems, and the ramifications for not responding to events on time can be life-critical."Multi-core processors very often lend to performance gains, and RTOS vendors are infusing operating systems with technologies and capabilities to take advantage of multiple cores. "VxWorks 653 now supports multi-core architectures, which will enable future designers to add even more applications to a single hardware platform," Wlad says. "Augmented with virtualization capability, our customers can add legacy applications based on Linux to an ARINC 653, DO-178C-certified environment. VxWorks technology supports open standards APIs, such as ARINC 653 and POSIX, and a wide variety of the industry’s latest multi-core architectures.""We've been tracking for some time the move to multi-core processors," says DDC-I's King, who is working to make the Deos operating system multi-core aware and multi-core capable. "From a safety-critical system developer point of view, those chips present some very interesting challenges -- in particular, regarding resource contention. I have software running on two cores competing for one memory subsystem -- there's resource contention. While one core is accessing it, the other one has to wait."What happens if core-zero has it tied up and core-one needs access to some critical data value because it has a critical calculation going on? All of a sudden, I have to wait. That's a bad thing," King continues. "We're bringing some unique, patented technology to bear that will address those challenges and allow our customers to leverage the full power afforded by these multi-core processors. Lacking that, you basically write software, run it on one core, and turn off all the other cores, so you're getting rid of a significant amount of the processing power. We want to bring this new technology to bear so that you can leverage all that power."CertificationIn mil-aero applications, safety and security are always paramount, says O'Dowd. "Before considering an RTOS for any safety related application, you should check its safety and security certifications.