Legion: A Worldwide Virtual Computer
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  Legion Overview
The wide-area virtual environment of the future

As computer networks are get larger, faster, and more powerful, they offer new opportunities. Gigabit networks, connecting powerful high-performance machines and workstations, have enormously powerful infrastructures that can solve complex problems and distribute huge amounts of information. Linked together, these connected resources make up a single, worldwide, virtual computer. We now need easy-to-use software that can manage a complex physical system and support large degrees of parallelism so that a virtual computer becomes a reliable, efficient, and real opportunity for a wide variety of users.

Legion, an object-based metasystems software project at the University of Virginia, is designed for a system of millions of hosts and trillions of objects tied together with high-speed links. Users working on their home machines see the illusion of a single computer, with access to all kinds of data and physical resources, such as digital libraries, physical simulations, cameras, linear accelerators, and video streams. Groups of users can construct shared virtual work spaces, to collaborate research and exchange information. This abstraction springs from Legion's transparent scheduling, data management, fault tolerance, site autonomy, and a wide range of security options.

As new requirements and new opportunities for distributed computing emerge and future users make unforeseen demands on resources and software, the demands placed on a virtual computer will evolve and grow. What works today or even tomorrow will soon be worse than useless, and we strongly believe that Legion should be a flexible tool that can adapt to new needs. Legion is therefore an open system, designed to encourage third party development of new or updated applications, run-time library implementations, and core components.

Legion in the computer

Legion sits on top of the user's operating system, acting as liaison between its own host(s) and whatever other resources are required. The user isn't bogged down with time-consuming negotiations with outside systems and system administrators, since Legion's scheduling and security policies act on his or her behalf. Conversely, it can protect its own resources against other Legion users, so that administrators can choose appropriate policies for who uses which resources under what circumstances. To allow users to take advantage of a wide range of possible resources, Legion offers a user-controlled naming system called context space, so that users can easily create and use objects in farflung systems. Users can also run applications written in multiple languages, since Legion supports interoperability between objects written in multiple languages.

The links below offer more specific information about key elements of the Legion system.

Link Description
Overview A general look at Legion
Objectives and constraints Legion's design objectives and restrictions
Applications Adapting and running Legion applications
Architecture Legion system architecture
High-performance computing Using Legion to get high-performance computing
Scheduling Scheduling and resource management
Security Legion's security philosophy and model


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This work partially supported by DOE grant DE-FG02-96ER25290, Logicon (for the DoD HPCMOD/PET program) DAHC 94-96-C-0008, DOE D459000-16-3C, DARPA (GA) SC H607305A, NSF-NGS EIA-9974968, NSF-NPACI ASC-96-10920, and a grant from NASA-IPG.