drivers remain a significant cause of system failures. In Windows XP, for example, drivers account for 85 % of recently reported failures. This article describes Nooks, a reliability subsystem that seeks to greatly enhance operating system (OS) reliability by isolating the OS from driver failures. The Nooks approach is practical: rather than guaranteeing complete fault tolerance through a new (and incompatible) OS or driver architecture, our goal is to prevent the vast majority of driver-caused crashes with little or no change to the existing driver and system code. Nooks isolates drivers within lightweight protection domains inside the kernel address space, where hardware and software prevent them from corrupting the kernel. Nooks also tracks a driver’s use of kernel resources to facilitate automatic cleanup during recovery. To prove the viability of our approach, we implemented Nooks in the Linux operating system and used it to fault-isolate several device drivers. Our results show that Nooks offers a substantial increase in the reliability of operating systems, catching and quickly recovering from many faults that would otherwise crash the system. Under a wide range and number of fault conditions, we show that Nooks recovers automatically from 99 % of the faults that otherwise cause Linux to crash.

In this paper we describe a new approach to implementing network protocols that enables them to have high performance and high flexibility, while retaining complete conformity to existing application programming interfaces. The key insight behind our work is that an application's interface to the network is distinct and separable from its interface to the operating system. We have separated these interfaces for two protocol implementations, TCP/IP and UDP/IP, running on the Mach 3.0 operating system and UNIX server. Specifically, library code in the application's address space implements the network protocols and transfers data to and from the network, while an operating system server manages the heavyweight abstractions that applications use when manipulating the network through operations other than send and receive. On DECstation 5000/200 This research was sponsored in part by the Advanced Research Projects Agency, Information Science and Technology Office, under the title "Research...

This dissertation analyzes the usefulness of existing "conventional" collaboration-transparency systems, which permit the shared use of legacy, single-user applications. I find that conventional collaboration-transparency systems do not use network resources efficiently, and they impose an inflexible, tightly coupled style of collaboration because they do not adequately support important groupware principles: concurrent work, relaxed WYSIWIS, group awareness, and inherently collaborative tasks. This dissertation proposes and explores solutions to those deficiencies. The primary goal of this work is to maintain the benefits of collaboration transparency while relieving some of its disadvantages. To that end, I present an alternate implementation approach that provides many features previously seen only in applications specifically designed to support cooperative work, called collaboration-aware applications. The new approach uses a replicated architecture, in which a copy of the application resides on each user's machine, and the users' input events are broadcast to each copy. I discuss solutions to certain key problems in replicated architectures, such as maintaining consistency, unanticipated sharing, supporting late-joiners, and replicating system resources (e.g., files, sockets, and random number generators). To enhance the collaborative usability of a legacy application, the new approach transparently replaces selected single-user interface objects with multi-user versions at runtime. There are four requirements of an application platform needed to implement this approach: process migration, run-time object replacement, dynamic binding, and the ability to intercept and introduce low-level user input events. As an instance of this approach, I describe its incorpor...

It has become increasingly difficult to drive a modern highperformance graphics accelerator at full speed with a serial immediate -mode graphics interface. To resolve this problem, retainedmode constructs have been integrated into graphics interfaces. While retained-mode constructs provide a good solution in many cases, at times they provide an undesirable interface model for the application programmer, and in some cases they do not solve the performance problem. In order to resolve some of these cases, we present a parallel graphics interface that may be used in conjunction with the existing API as a new paradigm for highperformance graphics applications.

This paper proposes an X Window System protocol compression scheme called Fast Higher Bandwidth X (FHBX). Previous X protocol compression schemes were either much slower (Higher Bandwidth X) or much less effective (Xremote). By using an application specific predictive hashing technique, FHBX is able to deliver three times the compression performance of Xremote, while running ten times as fast as HBX. The family of structured compression techniques illustrated by FHBX is applicable to other structured protocols, and should enable a host of interactive applications on low bandwidth wireless devices and telephone links. 1 Introduction This research is targeted at the vast numbers of networks which are, and which will continue to be, too slow. These networks include normal telephone connections, wireless connections, internet connections, and ISDN connections. If the current rate of increase in CPU performance holds, unloaded 10Mbit/sec Ethernet connections will be candidates for softwar...

In this paper we present Studierstube Workspace, an application framework which supports multiple users, multiple applications and multiple 3D and 2D interaction contexts in an augmented environment. We develop a design concept for collaborative working environments in virtual reality, especially the concept of multi-user aware applications and show how our implementation fits into this concept. Implementation details and application samples conclude the paper.

In this paper we present Studierstube Workspace, an application framework for augmented reality. We develop a concept for a collaborative working environments that simultaneously supports multiple users as well as multiple applications and in particular multi-tasking. The co-presence of multiple users interacting with multiple concurrently executing applications opens up new possibilities in the field of collaborative work. We describe how multiplicity in the interaction paths is used to implement the necessary underlying mechanisms and report on strategies and experiences regarding the development of multi-user aware applications. Keywords: computer graphics, virtual reality, augmented reality, collaborative user interfaces, multi-user systems, multitasking, Workspace Figure 1: Collaborative work in STUDIERSTUBE Workspace (composited image): 3D painting application window (with focus, middle) and object viewer window (w/o focus, lower right) 1. Introduction Technical progres...

Execution profiles are important in analyzing the performance of computer programs on a given computer system. However, accurate and complete profiles are difficult to arrive at for programs that follow the client-server model of computing, as in the popular X Window System. In X Window applications, considerable computation is invoked at the display server and this computation is an important part of the overall execution pro le. The profiler presented in this paper generates meaningful profiles for X Window applications by estimating the time spent in servicing the messages in the display server. The central idea is to analyze a protocol-level trace of the interaction between the application and the display server and thereby construct an execution profile from the trace and a set of metrics about the target display server. Experience using the profiler for examining bottlenecks is presented.

I have developed an X Protocol compression scheme called Higher Bandwidth X (HBX). This paper describes one aspect of HBX: POSTSCRIPT previewing. Using statistical models and arithmetic coding, HBX compresses the X protocol stream resulting from using ghostscript to preview documents by about 20:1, roughly 8 times the compression achieved by Xremote on the same stream. This is about 12 bits per source character after compression, implying a transmission time of about 3 seconds per page for normally formatted documents (3600 characters per page) using a standard 14400 bps modem. Introduction Higher Bandwidth X (HBX) is a compressed X protocol intended to provide improved interactive performance across low bandwidth interconnects such as serial lines. This paper describes the techniques used to achieve 20:1 lossless compression of the X protocol stream generated by the ghostscript POSTSCRIPT previewing program, when ghostscript is used to preview documents. The technique used to achiev...

TEX is an interactive, terminal based program, but today’s computing environment is increasingly window- and mouse-based. Dotex provides a “point and click ” wrapper around TEX and other tools in