Distributed operating systems

In the past five years, distributed operating systems research has gone through a consolidation phase. On a large number of design issues there is now considerable consensus between different research groups.\ud \ud In this paper, an overview of recent research in distributed systems is given. In turn, the paper discusses overall system structure, protection issues, file system designs, problems and solutions for fault tolerance and a mechanism that is rapidly becoming very important for efficient distributed systems design: hints.\ud \ud An attempt was made to provide sufficient references to interesting research projects for the reader to find material for more detailed study

Process Management in Distributed Operating Systems

As part of designing and building the Amoeba distributed operating system, we have come up with a simple set of mechanisms for process management that allows downloading process migration, checkpointing, remote debugging and emulation of alien operating system interfaces.\ud The basic process management facilities are realized by the Amoeba Kernel and can be augmented by user-space services: Debug Service, Load-Balancing Service, Unix-Emulation Service, Checkpoint Service, etc.\ud The Amoeba Kernel can produce a representation of the state of a process which can be given to another Kernel where it is accepted for continued execution. This state consists of the memory contents in the form of a collection of segments, and a Process Descriptor which contains the additional state, program counters, stack pointers, system call state, etc.\ud Careful separation of mechanism and policy has resulted in a compact set of Kernel operations for process creation and management. A collection of user-space services provides process management policies and a simple interface for application programs.\ud In this paper we shall describe the mechanisms as they are being implemented in the Amoeba Distributed System at the Centre for Mathematics and Computer Science in Amsterdam. We believe that the mechanisms described here can also apply to other distributed systems

Systems for the Nineties - Distributed Multimedia Systems

We live at the dawn of the information age. The capabilities of computers to store and look up information are only just beginning to be exploited. As little as ten years ago, practically all the information stored in computers was entered and retrieved in the form of text. Today, we are just starting to use other means of communicating information between people and machines -- computers can now scan images, they can record sound, they can produce synthesized speech, and they can show two- and three-dimensional images of spatial data. The realization that we are still at the beginning of the information age comes when we notice the vast difference between the way in which people interact with each other and the way in which people can interact with (or through) machines. When people communicate, they tend to use speech, gestures, touch, even smell; they draw pictures on the white board, they use text, pictures, photos, graphs, sometimes even video presentations. nterpersonal communication is truly multimedia communication in that it makes use of all our senses

You and I are Past Our Dancing Days

Operating systems have grown in size and functionality. Today's many flavours of Unix provide a multi-user environment with protection, address spaces, and attempts to allocate resources fairly to users competing for them, They provide processes and threads, mechanisms for synchronization and memory sharing, blocking and nonblocking system calls, and a complex file system. Since it was first introduced, Unix has grown more then a factor twenty in size. Several operating systems now consist of a microkernel, surrounded by user-space services [Accetta et al., 1986; Mullender et al., 1990; Rozier et al., 1988]. Together they provide the functionality of the operating system. This operating system structure provides an opportunity to make operating systems even larger. The trend for operating systems to grow more and more baroque was signalled more than a decade ago [Feldman, 1980], but has continued unabated until, today, we have OSF/1, the most baroque Unix system ever. And we have Windows/NT as a demonstration that MS-DOS also needed to be replaced by something much bigger and a little better.\ud In this position paper, I am asking what community we serve with our operating systems research. Should we continue doing this, or can we make ourselves more useful to society and industry by using our experience in operating systems in new environments.\ud I argue that there is very little need for bigger and better operating systems; that, in fact, most cPus will never run an operating system at all; and that our experience in operating systems will be better applied to designing new generations of distributed and ubiquitous applications

Distributed multimedia systems

Multimedia systems will allow professionals worldwide to collaborate more effectively and to travel substantially less. But for multimedia systems to be effective, a good systems infrastructure is essential. In particular, support is needed for global and consistent sharing of information, for long-distance, high-bandwidth multimedia interpersonal communication, greatly enhanced reliability and availability, and security. These systems will also need to be easily usable by lay computer users. \ud In this paper we explore the operating system support that these multimedia systems must have in order to do the job properly

Real-time disk scheduling in a mixed-media file system

This paper presents our real-time disk scheduler called the Delta L scheduler, which optimizes unscheduled best-effort disk requests by giving priority to best-effort disk requests while meeting real-time request deadlines. Our scheduler tries to execute real-time disk requests as much as possible in the background. Only when real-time request deadlines are endangered, our scheduler gives priority to real-time disk requests. The Delta L disk scheduler is part of our mixed-media file system called Clockwise. An essential part of our work is extensive and detailed raw disk performance measurements. The Delta L disk scheduler for its real-time schedulability analysis and to decide whether scheduling a best-effort request before a real-time request violates real-time constraints uses these raw performance measurements. Further, a Clockwise off-line simulator uses the raw performance measurements where a number of different disk schedulers are compared. We compare the Delta L scheduler with a prioritizing Latest Start Time (LST) scheduler and non-prioritizing EDF scheduler. The Delta L scheduler is comparable to LST in achieving low latencies for best-effort requests under light to moderate real-time loads and better in achieving low latencies for best-effort requests for extreme real-time loads. The simulator is calibrated to an actual Clockwise. Clockwise runs on a 200MHz Pentium-Pro based PC with PCI bus, multiple SCSI controllers and disks on Linux 2.2.x and the Nemesis kernel. Clockwise performance is dictated by the hardware: all available bandwidth can be committed to real-time streams, provided hardware overloads do not occur

Real Time in a Real Operating System

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Distributed match-making

In many distributed computing environments, processes are concurrently executed by nodes in a store- and-forward communication network. Distributed control issues as diverse as name server, mutual exclusion, and replicated data management involve making matches between such processes. We propose a formal problem called distributed match-making as the generic paradigm. Algorithms for distributed match-making are developed and the complexity is investigated in terms of messages and in terms of storage needed. Lower bounds on the complexity of distributed match-making are established. Optimal algorithms, or nearly optimal algorithms, are given for particular network topologies