Typical operating system design is marked by trade-offs between speed and reliability, features and security. Most systems are written in a low-level untyped programming language to achieve optimal hardware usage and for other practical reasons. But, this often results in CPU, memory, and I/O protection flaws due to mistakes in unverified code. On the other hand, fully verified systems are exceedingly hard to construct on any industrial scale. A high-level programming language, with an expressive type system suitable for systems programming, can help alleviate many of these problems without requiring the enormous effort of full verification.