This paper describes the concept of the operating system ERCOS (Embedded Real-time Control Operating System). ERCOS has been specially designed to meet the functionality and performance requirements in the area of automotive applications.The ever increasing functional requirements for modern electronic control units are introducing considerable complexity in the area of software development. It is well known that real-time operating systems provide powerful means to handle complex functions under real-time constraints. Past experience, however, has shown that the efficiency and flexibility of operating systems was very often inadequate for automotive applications.To overcome these insufficiencies the operating system ERCOS has been designed with dedicated support for automotive requirements. This has been achieved by supplementing the run-time part of the operating system by powerful off-line tools. The off-line tools support the construction of reusable and modular software in real-time applications by virtue of an object-based model and a strict separation of system-independent functional design and the run-time configuration. Furthermore, they allow the optimization of calls to the operating system to achieve very high efficiency.The major operating system concepts for scheduling, interprocess communication, guarantee of mutually exclusive access, timer handling and fault-tolerance as implemented in ERCOS are presented.Bosch will use ERCOS as a standard operating system platform for its automotive products. The operating system is compatible with the OSEK specification [OSE95] and has been passed to an independent software house 1 to make it available to third parties.