Operating System Organization

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Operating System Organization

• Chapter 3Michelle Grieco

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Outline

• Basic Functions of an OS
• Defining Requirements
• Implementation Considerations
• OS Kernels of Today
• Research in OS

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Purpose of an OS

• Creates abstractions
• Multiple processes compete for use of processor
• Coordination

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Responsibilities of an OS

• Create an abstract machine environment with
  multiple, autonomous, abstract components (that
  can be in use concurrently)
• Multiprogramming is used to create an abstract
  machine for each process
• Coordinate the use of the components according to
  the policies of the machines administrator
• Scheduler decides when and which processes get to
  use the processor

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Basic Requirements an OS Must Satisfy

• Device Management
• Process, Thread and Resource Management
• Memory Management
• File Management

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Device Management

• OS manages the allocation, isolation and sharing
  of devices according to policies chosen by the
  designer or system administrator.
• Devices treated in a general manner
• Special approaches for memory and processor

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Device Management
Device-Independent Part
Device-Dependent Part
Device-Dependent Part
Device-Dependent Part
Device
Device
Device
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Process, Thread and Resource Management

• Basic units of computation
• Elements of the computing environment needed by a
  process so that its threads can execute.

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Process Management

• Unix Style
• Includes management facilities to create,
  destroy, block, and run a process.
• Thread Based Approach
• More complicated since it has to manage processes
  and threads as separate entities

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Resource Manager

• Allocates resources to processes
• Handles requests for resources from threads
• Changes in status/changes in resource needs

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Memory Management

• Cooperates with process manager to allocate
  primary memory (executable or main) to each
  process
• Enforces isolation, methods to allow sharing of
  blocks of memory
• Virtual Memory allows processes to reference
  information stored on a storage device as if it
  were stored in primary memory.

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Memory Management
Memory Manager
Isolation and Sharing
Virtual Memory
Block Allocation
Process Manager
Storage Devices
Primary Memory
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File Management

• Why do we need a file manager?
• Provides an abstraction layer
• Distribution of information across networks

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OS Implementation Considerations Mechanisms

• Considerations
• Performance
• Exclusive Use of Resources
• Mechanisms
• Processor Modes
• Kernels
• Methods of Invoking Service

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Performance

• OS provides simplified programming interfaces
• Manage resource allocation sharing
• OS designers need to keep in mind
• What is the cost? Efficiency vs. Convenience
• How much do these abstractions slow down the
  execution of a program?
• What is the performance cost of using files
  rather than commands to directly manipulate
  storage devices?
• How much contribution to functionality of the
  system is derived versus the impact to
  performance?

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Exclusive Use of Resources

• Multiprogrammed systems support multiple
  processes and threads that need to share
  resources.
• Design Principles
• Do not to interfere with other processes
• Cannot use a resource unless it is specifically
  authorized to
• Allow both exclusive control to a process / or
  shared among a set of processes

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Exclusive Use of Resources

• Implementation of Design Principles includes
• Protection Mechanisms via security policies
• Defines strategies for managing resources
• File Protection Policy Example
• If OS enforces a policy, how do we prevent
  application software from overriding this policy?
• Trusted vs. Untrusted software and access
  barriers
• The kernel of the OS is trusted software
• All other software is untrusted

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Processor Modes

• The key hardware element for implementation of
  trusted software
• Mode Bit (supervisor or user)
• Supervisor (privileged, protected)
• Processor can execute every instruction
• User
• Processor can execute only a subset of all
  instructions

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Kernels

• What is a kernel?
• Design Decisions for what goes into the kernel?
• Everything but the kitchen sink?
• If it is in the kernel, it will have access to
  other parts of the kernel.
• If it is executed in user mode, it wont have
  access to kernel data structures.

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Requesting Services from the OS

• Techniques to request service
• System Call
• User invokes a trap instruction
• Message Passing
• User constructs a message that requests service

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System Call

• User invokes trap instruction when application
  calls stub program (uses reference to trap table)
  
• Processor is switched to supervisor mode
• Branches through trap table
• Executes function to be invoked
• OS finishes work and returns to user mode and
  returns control to user process.

Call ()
trap
return ()
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Message Passing

• Message constructed that requests service
  (message A)
• OS send() system call passes the message to
  trusted OS process (kernel).
• Executes trap
• Kernel executes function while user waits for
  result of service request. (message receive A)
• Kernel completes request it sends message B back
  to user process (send and receive B).

send (, A, )receive (, B, )
send/receive
receive (, A, )send (, B, )
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Logical Organization of OS
Process, Thread and Resource Manager
File Manager
Memory Manager
Device Manager
Processor(s)
Main Memory
Device(s)
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Kernels of Today

• UNIX
• Windows NT

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UNIX

• Goals
• Implement process, memory, file and device
  management in the kernel but only with minimal
  functionality to support a broad range of
  policies (bare essentials to read and write byte
  streams)
• Wanted to keep kernel as small as possible to
  improve efficiency
• Tailored further by use of application domains
  and application software to solve problems
• Result
• Very large software module including all managers
  (process, memory, file and device)
• Separate device drivers from kernel
• Evolved from swapping systems to paging
• Processing now addresses multiprocessor and
  distributed hardware configurations
• Implementations are difficult to modify
• IEEE POSIX.1 open systems standard
• No cost implementation LINUX

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WINDOWS

• Goals
• Extensible
• Portable
• Reliable
• Secure

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Summary

• Value of functionality built into the OS must
  justify the performance cost
• Modern OS includes managers for processes and
  resources including managers for memory, files,
  and devices
• Implementation techniques include the mode bit
  (supervisor/user) to ensure exclusive use of
  resources and to operate as trusted, system call
  interfaces and message passing mechanisms

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Research

• Here are some sites of interest on new and
  innovative advances in Operating Systems
• http//tunes.org/Review/OSes.html
• http//www.palmsource.com/palmos/ PalmOS Cobalt
  6.1 is the next generation of Palm OS. It will
  enable the creation of new categories of devices
  for the communications, enterprise, education and
  entertainment markets. Palm OS Cobalt 6.1
  provides integrated telephony features, support
  for WiFi and Bluetooth, and enhancements to the
  user interface.
• http//www.pdos.lcs.mit.edu/exo.html MITs AEGIS
  no runtime kernel, extreme performance gain
• http//www.cs.utah.edu/flux/ Flux Project at
  University of Utah build your own OS using OS
  bricks (an OS toolkit)
• http//srg.cs.uiuc.edu/2k/ 2K (formerly known as
  SPINE) is a distributed, reflective,
  component-based, adaptable operating system being
  built by researchers at the Systems Software
  Research Group from the University of Illinois at
  Urbana-Champaign and the Systems and
  Communications Group from the Universidad Carlos
  III - Madrid.
• http//www.acm.uiuc.edu/sigops/roll_your_own/
  write your own OS

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Questions

• You should be able to answer the following
  questions about this chapter
• 1. What is multiprogramming?
• 2. What are the four main managers in an OS and
  how do they interact?
• 3. What are the benefits to having an independent
  and dependent part of the device manager?
• 4. What is a process? What is a thread?
• 5. What are important considerations of a process
  manager?
• 6. What is virtual memory?
• 7. Why do we need a file manager? How is it
  useful?
• 8. What are OS implementation considerations?
  What are the mechanisms we can use to implement
  these considerations?
• 9. If OS enforces a policy, how do we prevent
  application software from overriding this policy?
• 10. What are the two techniques to request
  service? How do they work?

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Sources

• Nutt, G. Operating Systems, 3rd Edition. Addison
  Wesley. 2004
• http//tunes.org/Review/OSes.html
• http//www.palmsource.com/palmos
• http//www.pdos.lcs.mit.edu/exo.html
• http//www.cs.utah.edu/flux/
• http//srg.cs.uiuc.edu/2k/
• http//www.acm.uiuc.edu/sigops/roll_your_own/