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Experiences with the Amoeba Distributed Operating System
Andrew S. Tanenbaum Robbert van Renesse1 Hans van Staveren Gregory J. Sharp Dept. of Mathematics and Computer Science Vrije Universiteit De Boelelaan 1081 1081 HV Amsterdam, The Netherlands Internet: ast@cs.vu.nl, cogito@cs.vu.nl, sater@cs.vu.nl, gregor@cs.vu.nl Sape J. Mullender 2 Jack Jansen Guido van Rossum Centrum voor Wiskunde enInformatica Kruislaan 413 1098 SJ Amsterdam, The Netherlands Internet: sape@cwi.nl, jack@cwi.nl, guido@cwi.nl

The Amoeba distributed operating system has been in development and use for over eight years now. In this paper we describe the present system and our experience with it—what we did right, but also what we did wrong. Among the things done right were basing the system on objects, using asingle uniform mechanism (capabilities) for naming and protecting them in a location independent way, and designing a completely new, and very fast file system. Among the things done wrong were having threads not be pre-emptable, initially building our own homebrew window system, and not having a multicast facility at the outset. Computing Reviews categories: C.2.4, D.4 Keywords: Operating systems,Distributed systems, Distributed operating systems, Computer networks, Experience Descriptors: Network operating systems, Distributed applications, Distributed systems, Measurements General terms: Design, Experimentation, Performance
1. This research was supported in part by the Netherlands Organization for Scientific Research (N.W.O.) under grant 125-30-10.                           ¡¡¡¡¡¡¡¡¡¡¡¡¡  

-2INTRODUCTION The Amoeba project is a research effort aimed at understanding how to connect multiple computers together in a seamless way [15, 16, 26, 28, 32] The basic idea is to provide the users with the illusion of a single powerful timesharing system, when, in fact, the system is implemented on a collection of machines, potentially distributed among several countries. This researchhas led to the design and implementation of the Amoeba distributed operating system, which is being used as a prototype and vehicle for further research. In this paper we will describe the current state of the system (Amoeba 4.0), and tell some of the lessons we have learned designing and using it over the past eight years. We will also discuss how this experience has influenced our plans for thenext version, Amoeba 5.0. Amoeba was originally designed and implemented at the Vrije Universiteit in Amsterdam, and is now being jointly developed there and at the Centre for Mathematics and Computer Science, also in Amsterdam. The chief goal of this work is to build a distributed system that is transparent to the users. This concept can best be illustrated by contrasting it with a networkoperating system, in which each machine retains its own identity. With a network operating system, each user logs into one specific machine, his home machine. When a program is started, it executes on the home machine, unless the user gives an explicit command to run it elsewhere. Similarly, files are local unless a remote file system is explicitly mounted or files are explicitly copied. In short, theuser is clearly aware that multiple independent computers exist, and must deal with them explicitly. In a transparent distributed system, in contrast, users effectively log into the system as a whole, and not to any specific machine. When a program is run, the system, not the user, decides the best place to run it. The user is not even aware of this choice. Finally, there is a single, system widefile system. The files in a single directory may be located on different machines possibly in different countries. There is no concept of file transfer, uploading or downloading from servers, or mounting remote file systems. A file’s position in the directory hierarchy has no relation to its location. The remainder of this paper will describe Amoeba and the lessons we have learned from building...