Abstract

Our original view of X's use included highly mobile individuals (students moving between classes), and a hope, never generally realized for X, was the migration of applications between X servers. Toolkit implementers typically did not understand and share this poorly enunciated vision and were primarily driven by pressing immediate needs, and X's design and implementation made migration or replication difficult to implement as an afterthought. As a result, migration (and replication) was seldom implemented, and early toolkits such as Xt made it very difficult. Emacs is about the only widespread application capable of both migration and replication, and it avoided using any toolkit.

You should be able to travel between work and home or between systems running X at work and retrieve your running applications (with suitable authentication and authorization). You should be able to log out and ``park'' your applications somewhere until you retrieve them later, either on the same display, or somewhere else. You should be able to migrate your application's display from a handheld to a wall projector (for example, your presentation), and back again. Applications should be able to easily survive the loss of the X server (most commonly caused by the loss of the underlying TCP connection, when running remotely).

There are challenges not fully foreseen: applications must be able to adapt between highly variable display architectures. Changes to the X infrastructure in recent work make this retrofit into modern toolkits appear feasible, enabling a much more dynamic view of applications. Also, applications must be able to adapt between very different resolution displays (more than an order of magnitude) and differing pointing devices.

I cover the changes and infrastructure required to realize this vision, and hope to demonstrate a compelling part of this vision in action. This vision provides a much more compelling vision of what it means for applications to work in your network. With the advent of high speed metropolitan and wide area networks, and PDA's with high speed wireless networks, this vision will provide a key element of the coming pervasive computing system.

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