ITE 272 Introduction to ITE Part II

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ITE 272Introduction to ITE Part II

• Final Exam Review
• Chapters 11, 13 - Operating Systems IPC
• Chapter 12 File and Secondary Storage
  Management
• Linux Review

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Operating System Overview

• Operating System Management Functions
• Oversees all hardware resources and allocates
  them to user and applications as needed
• Performs many low-level tasks on behalf of users
  and application programs

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Operating System Overview
Operating system management functions.
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Operating System Overview

• Operating System Layers
• Command Layer (shell)
• The users interface to the operating system
• Service Layer
• Contains a set of functions called by application
  programs and the command layer
• Kernel
• Manages resources and directly interacts with
  computer hardware

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Operating System Overview
Layers of an Operating System
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Resource Allocation

• Resource Allocation Process
• Keeps detailed records of available resources
• Knows which resources are used to satisfy which
  requests
• Schedules resources based on specific allocation
  policies to meet present and anticipated demands
• Updates records to reflect resources commitment
  and release by processes and users

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Resource Allocation

• Single Process Resource Allocation
• operating system grants application control of
  all unused resources

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Resource Allocation

• Multiple Process Resource Allocation
• Multitasking OSs must be able to handle multiple
  programs and users simultaneously
• Manages hardware resources to
• Meet the resource needs of processes
• Prevent processes from interfering with one
  another
• Efficiently use hardware and other resources

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Resource Allocation

• Real and Virtual Resources
• Real resource
• Physical devices and associated system software
• Virtual resource
• Resources that are apparent to a process or user

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Process Management

• Process Control Data Structures
• A process is a unit of executing software that is
  managed independently by the operating system
• A process can request and receive hardware
  resources and operating system services

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Process Management

• Process Control Data Structures
• Process Control Block (PCB)
• Keeps track of each process by creating and
  updating a data structure
• The PCB is created when the process is created,
  updated when the process changes, and deleted
  when the process terminates.

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CPU Allocation

• Threads
• A portion (subdivision) of a process that can be
  scheduled and executed independently.
• Do not have their own resources
• In a multi-processor system threads are executed
  concurrently with the parent process

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CPU Allocation
Process/Thread movement among states
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CPU Allocation

• Scheduling is either preemptive, priority-based
  or real-time
• Preemptive Scheduling
• Forces applications to share the CPU whether they
  want to or not.
• The operating system parcels out CPU time slices
  to each program
• Every process is given a fixed time slice

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CPU Allocation

• Priority-Based Scheduling
• First-come first served
• The scheduler always dispatches the ready thread
  that has been waiting the longest.
• Explicit priority
• Uses a set of priority levels and assigns a level
  to each process or thread.

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CPU Allocation

• Priority-Based Scheduling (cont)
• Shortest Remaining Time Scheduling
• Chooses the next process to be dispatched based
  on the expected amount of CPU time needed to
  complete the process.

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CPU Allocation

• Interrupt Processing
• Occurs when a thread tries to access a resource
  that is not available
• Thread is placed in a blocked state
• If the event is correctable, thread remains in
  blocked state until it can be corrected
• If the event is not correctable, thread is halted

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Memory Allocation

• Memory is divided into areas called partitions
• Partitions are equal in size
• Usually 64KB

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Memory Allocation
memory allocation in a single-tasking operating
system.
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Memory Allocation

• Single-Tasking Memory Allocation
• Contiguous Memory Allocation
• The bulk of the operating system occupies lower
  memory addresses.
• The application program is loaded above the
  operating system.
• The remaining space is available for user
  programs and data.

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Memory Allocation
Noncontiguous memory allocation
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Memory Allocation

• Multitasking Memory Allocation Goals
• Allow as many active processes as possible.
• Respond quickly to changing memory demands of
  processes.
• Prevent unauthorized changes to a process memory
  region(s).
• Implement memory allocation and addressing as
  efficiently as possible.

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Memory Allocation
Several processes and operating system loaded
into 1MB fixed-size memory partitions
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Memory Allocation

• Memory Fragmentation
• As processes are created, executed, and
  terminated, memory allocation changes accordingly
• Memory partition allocation and deallocation
  leads to an increasing number of small free
  partitions separated by allocated partitions

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Memory Fragmentation
Changes in memory allocation as processes execute
and terminate
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Memory Allocation
Process 6 is allocated to noncontiguous memory
partitions
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Virtual Memory

• Mode of operating system memory management
• Uses secondary storage to extend capacity of
  primary storage
• Also called swap memory, swap space or paging
  memory

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Virtual Memory

• Programs are divided in 4KB segments called
  pages.
• Memory is divided in the same manner called
  page frames
• Secondary storage (swap space) is divided into
  page frames

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Virtual Memory

• Pages are allocated to page frames
• Memory or secondary storage
• Information about pages / page frames status are
  stored in page tables
• References made to page in memory is called a
  page hit
• References made to pages in secondary storage is
  a page fault

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Virtual Memory

• As space is needed, a page that needs to be
  written to a page frame is called a victim.
• Removed because of needed space
• Based on
• Least recently used
• Least frequently used

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Virtual Memory

• How does a process know where associated
  processes are in memory?
• GDT (Global Descriptor Table)
• Contains descriptors for all segments of a
  process
• LDT (Local Descriptor Table)
• Contains descriptors only for the process that
  the LDT was created for
• Points to Page Directory
• This method keeps a process from accessing any
  segments of memory other than its own

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Virtual Memory

• Processor keeps track of two other tables
• Page Directories table of pointers to page
  tables
• Contains an offset to allow the CPU to find the
  base physical address of the page
• Page Tables contains memory address of the page
  if loaded into memory
• Maps pages to page frames in the swap space
• Sets and clears page table in memory flags each
  time pages are loaded or swapped

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Virtual Memory
Relationship among segment and page (virtual
memory) tables
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Virtual Memory
Address resolution with virtual memory management
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Interprocess Communication

• Used in peer-to-peer communication protocols and
  distributed applications
• Provides method to allow programs to communicate
  with one another.
• Synchronize activities
• Exchange data

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Interprocess Communication

• Interprocess Signal
• Signals are messages, also known as an interrupt
• Sent between same process, independent processes
  or between OS and a process
• Usually are flags or single value data items

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Interprocess Communication

• Pipes
• FIFO buffer which enables concurrently executing
  process to communicate
• Output of process A is input for Process B
• Are shared memory locations that can be accessed
  by both processes
• Remote Procedure Calls
• When a process on one machine calls a process on
  another machine

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Chapter 12
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File Management System

• Collection of system software that performs file
  and secondary storage management and access
  functions
• Part of operating system
• May be supplemented by additional software

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File Management Systems

• Implemented in layers
• Command layer or application program
• File control
• Storage I/O control
• Secondary storage devices

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File Management Systems

• Logical and Physical Storage Views
• Logical Storage Views
• Viewed by users as a collection of files
  organized within directories and storage volumes
• Physical Storage Views
• Collection of physical storage locations
  organized as a linear address space

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Storage Allocation

• Allocation Units
• Smallest number of secondary storage bytes
  allocated to a file
• Cannot be smaller than the unit of data transfer
  between the storage device and controller, which
  is normally called a block
• Tradeoffs
• Efficient use of secondary storage space for
  files.
• Size of storage allocation data structures.
• Efficiency of storage allocation procedures

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Storage Allocation Table
Sample block diagram of a storage allocation
table. Records which allocation units are free
and which belong to files
Figure 12-9
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Storage Allocation
Directory entries for storage allocation table
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Storage Allocation
Storage allocation table matching storage
allocation shown in Fig 12-9
University of South Alabama - CIS ITE 272
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Storage Allocation

• Blocking and Buffering
• A logical record is a collection of data items,
  or fields, that is accessed by an application
  program as a single unit
• A physical record is the unit of storage
  transferred between the device controller and
  memory in a single operation

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Storage Allocation

• Blocking and Buffering
• Logical record grouping within multiple physical
  records is called blocking
• If a physical record contains just one logical
  record, then the file is said to be unblocked

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Storage Allocation
Sample of blocking logical records
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Storage Allocation

• Blocking and Buffering
• An FMS uses buffers in primary storage to store
  data temporarily as it moves between programs and
  secondary storage devices
• A buffer is a scratchpad for extracting logical
  records from physical records

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Storage Allocation
Reading of physical records to logical records
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Access Controls

• A File Management System helps prevent loss,
  corruption and unauthorized access to files.
• The operating system is used to identify and
  authenticate users and their processes.
• The file access is authenticated through ids and
  passwords.

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Access Controls

• UNIX defines three access control types
• Read
• Write
• Execute
• Windows NTFS permissions
• Advanced security options based on group or user
  name

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Linux Review
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Linux review

• File Management
• Command to change permissions on a directory or a
  file
• Parameters
• Display the contents of a string within a file
• Display the current working directory
• Delete a file or directory
• Navigate to a different directory
• Display the contents of a directory

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Linux review

• Create a new directory
• Rename a file or change its location
• Display the contents of a file (also to create a
  new file)

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Linux review

• User Management
• Create a new user account
• Remove a user account
• Location where user account info is stored
• Location where secure user info is stored
• Location where group info is stored

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Linux review

• Process Management
• Display a static list of all current running
  processes
• Display a dynamic list of current running
  processes
• Stop a running process
• Run a command with an adjusted scheduling
  priority
• Command to change the priority values of one or
  more running processes

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Linux review

• Boot process
• Where is the default runlevel specified?
• Directory containing the runlevel script files
• Other
• Client program to open a terminal session on a
  remote computer
• Command to configure a systems network settings

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Questions ?