Support for multimedia applications by general purpose computing platforms has been the subject of considerable research. Much of this work is based on an evolutionary strategy in which small changes to existing systems are made. The approach adopted here is to start ab initio with no backward compatibility constraints. This leads to a novel structure for an operating system. The structure aims to decouple applications from one another and to provide multiplexing of all resources, not just the CPU, at a low level. The motivation for this structure, a design based on the structure, and its implementation on a number of hardware platforms is described. I. Introduction G ENERAL purpose multimedia computing platforms should endow text, images, audio and video with equal status: interpreting an audio or video stream should not be a privileged task of special functions provided by the operating system, but one of ordinary user programs. Support for such processing on a platform on which ot...

In contemporary operating systems, continuous media (CM) applications are sensitive to the behaviour of other tasks in the system. This is due to contention in the kernel (or in servers) between these applications. To properly support CM tasks, we require “Quality of Service Firewalling” between different applications. This paper presents a memory management system supporting Quality of Service (QoS) within the Nemesis operating system. It combines application-level paging techniques with isolation, exposure and responsibility in a manner we call self-paging. This enables rich virtual memory usage alongside (or even within) continuous media applications. 1

Data Type. A collection of operations, each with a name and a signature defining the number and types of its arguments. application domain A domain whose purpose is to execute an application program. binding An association of a name with some value; in IDC, the local data structures for invoking an operation on an interface. class A set of objects sharing the same implementation. An object is an instance of exactly one class. closure The concrete realisation of an interface. A record containing two pointers, one to an operation table and the other to a state record. concrete type A data type whose structure is explicit. constructor An operation on an interface which causes the creation of an object, and returns the interfaces exported by the object. context A collection of bindings of names to values. context slot A data structure used to hold processor execution state within a domain. ix domain The entity which is activated by the kernel scheduler. Domains can be thought of a...

This paper describes a file system structure for supporting Quality of Service (QoS) guarantees. The device driver model clearly separates control- and datapath operations and presents a low-level of abstraction. The data-path module provides translation and protection of I/O requests enabling the file system layers to be executed as unprivileged code within shared libraries. Scheduling of low-level operations within the device driver is used to provide isolation between clients and Quality of Service guarantees. 1 Introduction A large proportion of the code executed on behalf of an application in a traditional operating system requires no additional privilege and does not, therefore, need to execute in a separate protection domain. Typically, code which must atomically and securely update important datastructures is rarely executed and usually associated with out-of-band operations such as opening or closing a file. It is only this code which must necessarily execute in a separate p...

A vertically structured Operating System is one in which neither the "kernel" nor "servers" perform work on behalf of applications -- the former because it exists only to multiplex the CPU, and the latter in order to avoid Quality of Service interference between the applications. Instead, wherever possible, the applications perform all of their own processing. Such a vertical structure provides many advantages for applications but leads to some interesting problems and opportunities for protocol stack implementation. This paper describes the techniques we used in our protocol implementation and the benefits that the vertical structure provided.

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This dissertation considers the problems associated with using Field Programmable Logic (FPL) within a processor to accelerate applications in the context of a general purpose workstation, where this scarce resource will need to be shared fairly and securely by the operating system between a dynamic set of competing applications with no prior knowledge of their resource usage requirements. A solution for these problems is proposed in the Proteus System, which describes a suitable set of operating system mechanisms, with appropriate hardware support, to allow the FPL resource to be virtualised and managed suitably without applications having to be aware of how the resource is allocated. We also describe a suitable programming model that would allow applications to be built with traditional techniques incorporating custom instructions. We demonstrate the practicability of this system by simulating an ARM processor extended with a suitably structured FPL resource, upon which we run multiple applications that make use of one or more blocks of FPL, all of which are managed by a custom operating system kernel. We demonstrate that applications maintain a performance gain despite having to share the FPL resource between other applications. This dissertation concludes that it is possible for an operating system to manage a reconfigurable processor within the context of a workstation environment, provided suitable hardware support, without negating the benefit of having the FPL resource, even during times of high load. It also concludes that the integration of custom hardware associated with applications into the system is manageable within existing programming techniques. i Acknowledgements The following people must be acknowledged for their help and support: • My supervisor team, which seems to have a higher turnover rate than expected (in alphabetical

Modern desktop and server computer systems use multiple processors: general purpose CPU(s), graphic processor (GPU), network processors (NP) on Network Interface Cards (NICs), RAID controllers, and signal processors on sound cards and modems. Some of these processors traditionally have been special purpose processors but there is a trend towards replacing some of these with embedded general purpose processors. At the same time main CPUs become more powerful; desktop CPUs start featuring Simultaneous Multi-Threading (SMT); and Symmetric Multi-Processing (SMP) systems are widely used in server systems. However, the structure of operating systems has not really changed to reflect these trends --- different types of processors evolve at different timescales (largely driven by market forces) requiring significant changes to operating systems kernels to reflect the appropriate tradeoffs.

Virtual machines (vms) have enjoyed a resurgence as a way of allowing the same application program to be used across a range of computer systems. This flexibility comes from the abstraction that the vm provides over the native interface of a particular computer. However, this also means that the application is prevented from taking the features of particular physical machines into account in its implementation. This dissertation addresses the question of why, where and how it is useful, possible and practicable to provide an application with access to lower-level interfaces. It argues that many aspects of vm implementation can be devolved safely to untrusted applications and demonstrates this through a prototype which allows control over run-time compilation, object placement within the heap and thread scheduling. The proposed architecture separates these application-specific policy implementations from the application itself. This allows one application to be used with different policies on different systems and also allows nave or premature optimizations to be removed.

This is an interim report on the investigations into securing Asynchronous Transfer Mode (ATM) networks. We look at the challenge in providing such a secure ATM network and identify the important issues in achieving such goal. In this paper, we discuss the issues and problems involved and outline some techniques to solving these problems. The network environment is first examined and we also consider the correct placement of security mechanism in such an environment. Following the analysis of the security requirement, we introduce and describe a key agile cryptographic device for ATM. The protection of the ATM data plane is extremely important to provide data confidentiality and data integrity. Techniques in providing synchronisation, dynamic key change, dynamic initialisation vector change and Message Authentication Code on ATM data, are also being considered. Next, we discuss the corresponding control functions. A few key exchange protocols are given as possible candidates ...