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Review: Chapters 1

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Review: Chapters 1 7 – PowerPoint PPT presentation

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Title: Review: Chapters 1


1
Review Chapters 1 7
2
Chapter 1
  • OS is a layer between user and hardware to make
    life easier for user and use hardware efficiently
  • Control program or resource allocator
  • Computer organization
  • CPU(s), memory, and I/O devices connect to a
    common bus
  • Devices request CPU attention through interrupts
  • Storage hierarchy speed, cost, volatility
  • Caching copy frequently used data to faster
    storage
  • Multiprogramming multiple jobs in memory ?
    efficiency
  • Timesharing frequently switch between jobs ?
    interactive, short response time ? users get the
    impression that each has his/her own computer
  • Dual mode operation user and kernel modes
  • Protect OS and users from each other
  • Privileged instructions executed only in kernel
    mode
  • Timer to prevent processes from holding resources
    forever

3
Operating-System Operations
  • OS is interrupt driven it sits idle till
    something happens
  • Interrupts are generated by devices (hardware)
  • Traps (or exceptions) are software-generated
    interrupts due to
  • software errors, e.g., divide by zero
  • Request for operating system services (system
    calls)
  • Dual-mode operation allows OS to protect itself
    and other system components
  • User mode and kernel mode
  • Mode bit provided by hardware
  • Provides ability to distinguish when system is
    running user code or kernel code
  • Some instructions designated as privileged, only
    executable in kernel mode
  • System call changes mode to kernel, return from
    call resets it to user

4
Transition from User to Kernel Mode
5
Chapter OS Services and Structures
  • OS provides two sets of services for
  • user convenience and
  • efficient use of resources
  • System calls programming interface to OS
    services
  • Typically used through APIs for portability and
    ease
  • OS structures
  • monolithic
  • layered
  • microkernel
  • modular

6
Chapter 3 Processes
  • Process is a program in execution
  • OS maintains process info in PCB
  • Process State diagram
  • Creating and terminating processes (fork)
  • Process scheduling
  • Long-, short-, and medium-term schedulers
  • Scheduling queues

7
Scheduling The Big Picture (contd)
In most small and interactive systems (UNIX,
WinXP, ), only the CPU scheduler exists
8
Process Lifetime
9
CPU Switch From Process to Process(Context
Switch)
  • When switching occurs, kernel
  • Saves state of P0 in PCB0 (in memory)
  • Loads state of P1 from PCB1 into registers
  • State values of the CPU registers, including
    the program counter, stack pointer

10
Interprocess Communications Models
Message Passing
Shared Memory
11
Chapter 4 Threads
  • A thread is a basic unit of CPU utilization, a
    process is composed of one or more threads
  • Each thread has Program counter, stack,
    registers
  • Threads share code, data, OS resources (e.g.,
    open files and signals)

12
Single and Multithreaded Processes
13
User level threads vs. kernel threads
14
Chapter 5 CPU Scheduling
  • Process execution cycle of CPU bursts and I/O
    bursts
  • CPU bursts lengths many short bursts, and few
    long ones
  • Scheduler selects one process from ready queue
  • Dispatcher performs the switching
  • Scheduling criteria (usually conflicting)
  • CPU utilization, waiting time, response time,
    throughput,
  • Scheduling Algorithms
  • FCFS, SJF, Priority, RR, Multilevel Queues,

15
First-Come, First-Served (FCFS) Scheduling
  • Process Burst Time
  • P1 24
  • P2 3
  • P3 3
  • Suppose that the processes arrive in the order
    P1 , P2 , P3 The Gantt Chart for the schedule
    is
  • Waiting time for P1 0 P2 24 P3 27
  • Average waiting time (0 24 27)/3 17

16
Multilevel Feedback Queues
17
CPU Scheduling
  • Multiprocessor Scheduling
  • Processor affinity vs. load balancing
  • Evaluation of Algorithms
  • Modeling, simulation, implementation

18
Chapter 6 Synchronization
  • Processor Synchronization
  • Techniques to coordinate access to shared data
  • Race condition
  • Multiple processes manipulating shared data and
    result depends on execution order
  • Critical section problem
  • Three requirements mutual exclusion, progress,
    bounded waiting
  • Software solution Petersons Algorithm
  • Hardware support TestAndSet(), Swap()
  • Busy waiting (or spinlocks)
  • Semaphores
  • Not busy waiting
  • wait(), signal() must be atomic ? moves the CS
    problem to kernel

19
Synchronization
  • Some classical synchronization problems
  • Consumer-producer
  • Dining philosopher
  • Readers-writers

20
Chapter 7 Deadlock
  • A set of blocked processes each holding a
    resource and waiting to acquire a resource held
    by another process in the set
  • Four necessary (but not sufficient) conditions
  • Mutual exclusion only one process at a time can
    use a resource
  • Hold and wait a process holding at least one
    resource and is waiting to acquire additional
    resources held by other processes
  • No preemption a resource can be released only
    voluntarily by the process holding it, after that
    process has completed its task
  • Circular wait there exists a set P0, P1, ,
    P0 of waiting processes such that P0 is waiting
    for a resource that is held by P1, P1 is waiting
    for a resource that is held by
  • P2, , Pn1 is waiting for a resource that is
    held by Pn, and P0 is waiting for a resource
    that is held by P0

21
Deadlock Handling
  • Prevention ensure that at least one of the
    necessary conditions does not hold
  • Avoidance decide for each request whether or not
    the issuing process should wait to avoid leaving
    the system in unsafe state
  • Resource-allocation graph single instance of a
    resource type
  • Bankers algorithm multiple instances of a
    resource type
  • Detection and Recovery
  • Detection algorithm
  • Recovery process termination or resource
    preemption

22
  • Good Luck on the Exam!
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