This paper describes an operating system for safe execution of hard real-time and non real-time tasks on a single computer. Achieving this goal requires not only to follow the traditional behavioral security principles, but also new resource security principles throughout the system. Even if these principles put heavy constraints on the system, they make allocation predictable, immune from denial of service attacks, and allows ensuring a task will have enough resource to complete its execution. We prove that building resource-secure systems is pos-sible by describing the design and implementation of our prototype, Anaxagoros. The main issue for writing the system is synchronization, and we propose several novel ways to solve synchronization problems.