Ningning Hu Legion: An Operating System for Wide-Area Computing Grimshaw, A.; Ferrari, A.; Knabe, F.; Humphrey. This paper talks about the architecture of a system which can support wide-area computing by abstracting the system components into different types of objects. The first contributions of this paper is the identification of the requirements of wide-area computing applications: being good at complexity management, having single system image, being able to use in multiple organizations, being able to deal heterogeneous resources, good scalability, strong fault tolerance, supporting multi-language and legacy applications, good security. Legion solves the above problem from high level software point of view. It structures a system as a collection of distributed objects, all of which communicate with another using a uniform remote method invocation service. These objects can be classified into five categories: resource representation and management (mainly includes host objects and vault objects, providing system extensibility and site autonomy), task/object management (in the charge of all kinds of Class Managers), three-layer naming mechanism (Object Address -- OA, Legion Object Identifiers -- LOID, and context space), object based extensible file system, interprocess communication (macro-dataflow is used to reducing interprocess communication and tolerating high latencies). Legion's security mechanism is embedded in the implementation of objects, which includes using a mandatory internal method MayI for access control. This paper discusses the fundamental difference and relationship between Legion and four other distributed computing system: Globe, Globus, CORBA, and World Wide Web, emphasizing the design philosophy of Legion -- develop system software that can provide high level system abstractions, reducing the complexity from application's point of view. >From the information in this paper, the system discussed focuses on reducing the difficulty in developing and managing "large" distributed system resources, by adding another "layer" on current operation system. The most straightforward question for it is how it is going to affect operating system's performance. Although quite a few applications are described, nothing about performance is mentioned.