EROS

Extremely Reliable Operating System (EROS) is an operating system developed starting in 1991 at the University of Pennsylvania, and then Johns Hopkins University, and The EROS Group, LLC. Features include automatic data and process persistence, some preliminary real-time support, and capability-based security. EROS is purely a research operating system, and was never deployed in real world use. , development stopped in favor of a successor system, CapROS. Key concepts The overriding goal of the EROS system (and its relatives) is to provide strong support at the operating system level for the efficient restructuring of critical applications into small communicating components. Each component can communicate with the others only through protected interfaces, and is isolated from the rest of the system. A protected interface, in this context, is one that is enforced by the lowest level part of the operating system, the kernel. That is the only part of the system that can move information from one process to another. It also has complete control of the machine and (if properly constructed) cannot be bypassed. In EROS, the kernel-provided mechanism by which one component names and invokes the services of another is a capability, using inter-process communication (IPC). By enforcing capability-protected interfaces, the kernel ensures that all communications to a process arrive via an intentionally exported interface. It also ensures that no invocation is possible unless the invoking component holds a valid capability to the invoked component. Protection in capability systems is achieved by restricting the propagation of capabilities from one component to another, often through a security policy termed confinement. Capability systems naturally promote component-based software structure. This organizational approach is similar to the programming language concept of object-oriented programming, but occurs at larger granularity and does not include the concept of inheritance. When software is restructured in this way, several benefits emerge: The individual components are most naturally structured as event loops. Examples of systems that are commonly structured this way include aircraft flight control systems (see also DO-178B Software Considerations in Airborne Systems and Equipment Certification), and telephone switching systems (see 5ESS switch).