COSY - a system specification language based on paths and processes. A new notation for specifying systems of concurrent processes sharing distributed systems of resources is introduced and the utility of the notation is demonstrated by defining novel, highly concurrent and distributed algorithms performing important operating system functions. The notation permits a clear and logical development of the algorithms from an analysis of its component notions; such as various buffer types, as well as non-priority and priority resource management strategies; without any reference to implementation detail. This property of the notation facilitates both the validation of the algorithms as well as their novel, highly concurrent and distributed implementation.