Work on the Pegasus project finished in October 1995. For current information refer to the web pages for the follow-on project, Pegasus II. The text below was last updated in August 1995.
The Pegasus project (Esprit BRA 6865) is a collaborative research
effort with the University of Twente (NL). The official title of the
project is "Operating system support for distributed interactive
multimedia", and the work is organised as four work packages:
Pegasus is producing an entirely new operating system, whose design is geared
to support of high-performance applications which require a consistent
quality of service, such as those which use multimedia. This
operating system, called Nemesis, is currently being implemented for
DECstation (MIPS R3000-based) and DEC AXP-based workstations. Related systems
are being developed for two different types of ARM-based machine.
Nemesis is a single-address-space system, with an extremely light-weight
kernel ('Nemesis Trusted Supervisor Code', or NTSC), and strong emphasis on
performing operating system functions in the user's domain (thus avoiding the
need for expensive protection regime changes).
An outline of the thinking behind the structure of Nemesis is to be found in
the Kernel
report on the laboratory's ftp server. A copy of Eoin Hyden's Ph.D.
thesis is also available from there; Eoin worked in the Pegasus project
during the latter stages of his research here.
The project has developed an interface definition language called Middl, in
which interfaces to the Nemesis operating system (as well as to other services
that the project defines) are specified. The specification of
Middl (also known as Pegasus
paper 94-16) is also available from the laboratory's ftp server.
The interface specifications of a `recent' version of Nemesis are
available, formatted, as `Nemesis
Structure and Interfaces' (also known as Pegasus
paper 94-17).
Return to index of work packages
The Huygens file server and associated naming (and other) services are being
developed within the Pegasus project by the Twente group. The Huygens File
Server will have to cater both to the needs of multimedia applications --- high
data rates with minimal jitter --- and those of distributed applications ---
good consistency semantics, high reliability in the presence of failures.
The structure of the system incorporates ideas from many previous storage
architectures, including log-structure file systems, RAID storage
architectures, token-based synchronisation of access, etc.
Return to index of work packages
The view of the project is that communications support for multimedia has to be
based on ATM-style networks. The present work in communications support
involves installing ATM networks (currently, the Cambridge University
Fairisle local-area network switches with Olivetti Research
YES host interfaces) and providing operating system support for them.
Ultimately, the project hopes to integrate the local-area ATM networks with
some wide-area service; such a connection should offer a valuable test both of
quality of service provision over a wide-area ATM network, and of the support
services that have been implemented within the Nemesis system.
Return to index of work packages
The purpose of the Application work package is to provide a demonstration
test-bed that will let us show off the results of our work. All that we've
done so far under this package has been experimental work under the Cambridge
Micro-kernel system Wanda, and construction of application
infrastructure.
The project proposal suggested a demonstrator called The Digital TV
Director. Such an object would control cameras and microphones, and
screen images and loudspeakers to enable seamless operation of a distributed
computer-controlled multimedia conference. Underlying technologies would
include audio location of speakers, computer control of camera pan and tilt,
and of course networks and operating systems that offer the required quality of
service to an application that knows what to make of all its input.
Operating system work package
File system work package
Communications support work package
Application work package