A computing system that is universally accessible and is able to harness networked resources a,s and when necessary ca,n be said to provide computing on demand. This report describes and evaluates the design of a network desktop infrastructure tha,t provides access to distributed operating system services via standard world-wide web lsrowsers. Unmodified browsers can be used to access and use the desktop because it zippears as a normal web server to t'hem; the semantics associated with computing services are supported by treating URLs as locations in a dynamic, virtual, and sideeffect based address space. The desktop interface is not hard-wir'ed to the characteristics of any specific tool; the use of a programmable state machine in conjunction with a illechanism that embeds varia,bles and objects within standa1,rd HTML allow the desktop to dynamically generate interfaces for tools and to ern-ulate interactivity. Finally, users do not need physical accounts on the resources utilized by the desktop infrastructure; logical user accounts are created and managed with the help of filesystem and cache proxies, and the use of shadow accounts and software fault isolation techniques. The described infrastructure serves as the front end for the Purdue University Network Computing Hubs (PUNCH), a widely used demand-based network-computing system that allows users to access a,nd run unmodified software tools via world-wide web browsers.
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