No abstract available.

The goal of the Argo system is to allow medium-sized groups of users to collaborate remotely from their desktops in a way that approaches as closely as possible the effectiveness of face-to-face meetings. In support of this goal, Argo combines high quality multi-party digital video and full-duplex audio with telepointers, shared applications, and whiteboards in a uniform and familiar environment. The shared applications can be unmodified X programs shared via a proxy server, unmodified groupware applications, and applications written using our toolkit. Workers can contact each other as easily as making a phone call, and can easily bring into a conference any material they are working on. They do so by interacting with an object-oriented, client/server conference control system. The same conference control system is used to support teleporting, i.e. moving the desktop environment from one workstation's display to another (for example, from office to home). This paper describes the system we have built to test the hypothesis that the effectiveness of remote collaboration can be substantially impacted by the responsiveness of the interaction media.

In this paper we describe restartable atomic sequences, an optimistic mechanism for implementing simple atomic operations (such as Test-And-Set) on a uniprocessor. A thread that is suspended within a restartable atomic sequence is resumed by the operating system at the beginning of the sequence, rather than at the point of suspension. This guarantees that the thread eventually executes the sequence atomically. A restartable atomic sequence has significantly less overhead than other software-based synchronization mechanisms, such as kernel emulation or software reservation. Consequently, it is an attractive alternative for use on uniprocessors that do no support atomic operations. Even on processors that do support atomic operations in hardware, restartable atomic sequences can have lower overhead.

In early 1977 we began to design the concurrent programming facilities of Pilot, a new operating system for a personal computer [5]. Pilot is a fairly large program itself (25,000 lines of Mesa code). In addition, it supports some large applications, ranging from data base management to internetwork message transmission, which are heavy users of concurrency (our experience with some of these applications is discussed in the paper). We intended the new facilities to be used at least for the following purposes:

The Pilot operating system is designed for the personal computing environment. It provides a basic set of services within which higher-level programs can more easily serve the user and/or communicate with other programs on other machines. Pilot omits certain functions sometimes associated with “complete” operating systems, such as character-string naming or user-command interpretation; higher-level software provides such facilities as needed. On the other hand, Pilot provides a higher level of service than that normally associated with the “kernel” or “nucleus” of an operating system. Pilot is closely coupled to the Mesa programming language and runs on a rather powerful personal computer, which would have been thought sufficient to support a substantial timesharing system of a few years ago. The primary user interface is a high resolution bit-map display, with a keyboard and a pointing device. Secondary storage generally takes the form of a sizable local disk. A local packet network provides a high bandwidth connection to other personal computers, and to server systems offering such remote services as printing and shared file storage.