Chorus Vs Unix Operating Systems

1
Chorus Vs Unix Operating Systems

• Overview
• Introduction
• Design Principles
• Programmer Interface
• User Interface
• Process Management
• Memory Management
• File System
• Inter Process Communication
• Summary Conclusions
• References

2
Introduction

• Unix Operating System
• Originally developed in a laboratory at ATTs
  Bell Labs.
• Unix is a mature, technically superior group of
  operating systems with extremely powerful
  multiprocessor server hardware.
• Unix is a monolithic operating system.
• Chorus Operating System
• Chorus was a research project on distributed
  systems at INIRA in France. It was bought by Sun
  Microsystems in 1997.
• The Chorus operating system is a highly scalable
  and reliable embedded operating system.
• Chorus is a micro kernel-based operating system.
  

3
Design Principles - Unix

• Unix is a layered operating system.
• The operating system, referred to in Unix as the
  kernel, interacts with the hardware and provides
  the services to the user programs.
• It is a multi-user, multi-tasking operating
  system.

4
Design Principle - Chorus

• A Chorus system is composed of a small nucleus
  and a set of system servers, which cooperate in
  the context of subsystems.
• Chorus Nucleus is not the core of a specific
  operating system rather it provides generic
  tools designed to support a variety of host
  subsystems, which can coexist on top of the
  Nucleus.
• This structure supports application programs,
  which already run on an existing operating
  system, by reproducing the operating systems
  interface within a subsystem.

5
Process Management

• Unix
• Every process running under UNIX is identified by
  a process- id (pid), an integer value. Each
  process is identified with the owner of the
  process, simply called uid.
• Processes are arranged in a tree structure link.
• Unix is a timesharing system. Each turn is a
  called a timeslice.
• Chorus
• A process in Chorus defines a protected address
  space.
• Every process has a protection identifier
  associated with it.
• There are three kinds of processes in Chorus,
  each having different execution privileges.
  Supervisor processes, System processes and User
  processes.

6
Memory Management

• Unix
• All memory assigned as pages
• Each user process works in a virtual 4GB memory
  space
• Multi-User nature of UNIX requires that no memory
  be allocated to absolute locations 
• Unix memory management is based on Demand-paged
  virtual memory system.
• It employs the Least Recently Used algorithm.

7
Memory Management

• Chorus
• Abstract memory objects are typically provided to
  protect regions of memory. Virtual memory
  management may be implemented as part of the
  kernel or user-level process. 
• The Unit of data abstraction in Chorus is called
  the segment. Segments generally represent some
  form of secondary storage such as a file.  
• Each process address space is divided into
  regions. A region is a contiguous range of
  virtual addresses within a process, which maps a
  portion of a segment to a given virtual address.
   
• System processes known as mappers are responsible
  for mapping segments onto regions. If a process
  makes a request to read or modify data within a
  region, the mapper returns the appropriate
  segment containing the data.

8
File System

• Unix
• The UNIX file system is one of the simplest tree
  structured file systems to use.
• There are no syntax extensions for accessing
  system files, files belonging to other users, or
  files on network mounted file systems.
• The file system is one place where UNIX has a
  friendlier user interface than most systems.
• Chorus
• The Chorus file system is very familiar to the
  Unix file system but it provides a file manager.
• The file manager acts as a mapper for the Chorus
  kernel and also performs Unix file system
  management.
• The Chorus file system has the standard Unix
  code, code to support Chorus segment mapper, and
  codes to catch hardware interrupts and map them
  onto hardware device drivers.

9
Inter-Process Communication

• Unix
• Processes in Unix based systems communicate
  between themselves through IPC constructs. Among
  these are
• Pipes
• FIFO (named pipes)
• Streams (Files)
• Sockets
• Messages Exchange messages with any process or
  server.
• Semaphores Allow unrelated processes to
  synchronize execution.
• Shared memory Allow unrelated processes to share
  memory.
• Chorus
• Communication services provided by Chorus are 
• Asynchronous Message-passing
• Does not guarantee delivery of message.
• No notification to sender.
• Synchronous RPC
• Client-Server model.
• Guarantees delivery of message.
• Notification send to sender

10
Protection and Security

• Unix
• Physical Security
• Network Security
• Account Security
• File System Security
• Chorus
• Security in Chorus is offered by the application
  level.
• There is no security in the Chorus nucleus.
• Chorus has provisions for the development of
  secure distributed systems through support for
  access control and authentication.
• Security is offered in Chorus by the concept of
  unique identifiers.
• Knowledge of Unique Identifier gives full
  privileges to manipulate the object.

11
Conclusion

• Unix cannot fulfill the expectations of system
  builders if it continues to increase in
  complexity without a well-defined modular
  architecture, based on simple concepts, to manage
  its growth.
• Therefore micro-kernel based distributed
  operating systems such as Chorus came into
  existence.