CS 550

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CS 550

• Amoeba-A Distributed Operation System
• by
• Saie M Mulay

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Introduction

• A Brief History
• 1970s Timesharing (1 computer with many
  users)
• 1980s Personal computing (1 computer per user)
• 1990s Parallel computing (many computers per
  user)
• Amoeba is a Parallel/Distributed Operating System.

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What is Amoeba?

• Amoeba is designed to take a collection of
  machines and make them act together as a single
  integrated system.
• It is a powerful microkernel based system that
  turns a collection of workstations or single
  board computers into a distributed system

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Topics Covered

• Hardware Architecture
• Software Architecture
• Design Goals and Chief Design Features
• Protection and Capabilities
• File System
• Process Management

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Hardware Architecture

• 4 Major Components
• Workstations
• Local Area Network
• Gateway
• Processor Pool

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Hardware Architecture contd...

• Flip Network Protocol for LAN communication.
• Highly Reliable Architecture
• User can be assigned 10-100 processors.
• The Amoeba operating system is natively
  programmed for Suns, VAXs and Motorola chips
• Minimum configuration for a SPARC station system
• File Server 16 MB RAM, a 300 MB disk, a SCSI
  tape drive.
• Workstation 8 MB RAM, monitor, keyboard, and
  mouse.
• Pool processor 8 MB RAM

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Software Architecture

• Client-Server Paradigm.
• Object and Class based architecture.
• Associated with each object is a class. Classes
  may contain other classes and therefore are
  hierarchical in nature. This inheritance creates
  the object interface for object manipulation such
  as deleting, read, write, append, etc
• Uses Remote Procedure Calls.
• These calls are in the form of light weight
  processes.

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Software Architecture contd...

• There are 3 basic system calls available to a
  user process.
• do_operation Client sends a request message and
  receives a reply the header contains a
  capability for the object upon which an operation
  is being requested.
• get_request Server sends a request from the
  port specified in the message header.
• put_reply Server replies

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Design Goals and Chief Design Features

• Network transparency
• All accesses to the network are user
  transparent.
• Object-based resource management
• All resources are regarded as objects.
• All Objects are managed by servers.
• User-level servers
• The system software was to be constructed as far
  as possible as a collection of servers executing
  at user-level, on top of a standard microkernel
  that was to run at all computers in the system,
  regardless of their role

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Protection and Capabilities

• In Amoeba all resource identifiers are
  capabilities, implemented in the form shown
  below
• Server Port Request Messages are received on
  this port.
• Object Number Used to identify the object within
  that server.

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Protection and Capabilities contd..

• Permissions It defines the owner capabilities.
• Check Field Its a 48 bit random number assigned
  when the object is created. There are 248 i.e.
  about 1014 combinations of 48 bit wide fields.
  Generating and testing all these combinations by
  brute force would involve passing each guess in a
  message to the server, at about 2 milliseconds
  for each guess. That is about 2 x 1011 seconds,
  or about 6,300 years.

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File System

• Naming is an intrinsic part of object
  capabilities in an Amoeba O.S.
• There is an extra level of mapping from
  symbolic, hierarchical path names to
  capabilities.Hence user sees local objects as
  public objects.
• Members of a group may be given capability of a
  directory.
• In reality directories are name/capability
  pairs.

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File System contd...

• Operations Supported Read Create and Delete.
• Write Operation not supported. Hence files
  cannot be changed once they are created. Thus
  files can be stored contiguously resulting in
  efficient file storage.
• High security and Reliability
• All internal tables are replicated.
• Directory protection using encryption key
• No cache coherency
• Information cached by the directory service
  never gets outdated.

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Process Management

• Processes are made up of one or more lightweight
  processes called threads to minimize context
  switching.
• Process address is encapsulated in an internal
  memory map.
• This map has an entry for every segment of
  address for a potential process. An entry
  contains the virtual address, segment length,
  segment mapping, and capability of the object
  from which the segment is initialized.

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Process Management contd..

• Thread map that describes initial state of
  thread, processor status, program counter, stack
  pointer, the stack base, register values, and the
  system call state.
• Processes can have 2 possible states
• Stunned - When the process is being debugged.
• Running

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Machines On Which Amoeba Runs

• Amoeba currently runs on the following
• architectures
• Sun 4c and MicroSPARC SPARC stations
• Intel 386/486/Pentium/Pentium Pro (IBM AT bus,
  PCI Bus)
• 68030 VME-bus boards (Force CPU-30)
• Sun 3/60 Sun 3/50 workstations

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Pricing

• Amoeba is available free to universities that
  have FTP or WWW access to the Internet, and for
  US 500 on Exabyte or DAT tape to those that do
  not. Printed sets of the manuals can be obtained
  for US 500 each.

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Conclusion

• The Amoeba can be built with off the shelf
  products, and produces a very high performance
  operating system without custom made parts. The
  Amoeba operating system in general is a highly
  secure, high performance distributed operating
  system.