1. Review: Chapters 1 – 7

2. 1.2 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. 1.3 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. 1.4 Transition from User to Kernel Mode

5. 1.5 Chapter 2: 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. 1.6 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. 1.7 Scheduling: The Big Picture Disk Jobs Job sched.CPU sched. Midterm sched. In most small and interactive systems (UNIX, WinXP, …), only the CPU scheduler exists

8. 1.8 Process Lifetime

9. 1.9 CPU Switch From Process to Process (Context Switch) When switching occurs, kernel Saves state of P 0 in PCB 0 (in memory) Loads state of P 1 from PCB 1 into registers State = values of the CPU registers, including the program counter, stack pointer

10. 1.10 Interprocess Communications Models Message Passing Shared Memory

11. 1.11 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. 1.12 Single and Multithreaded Processes Shared among threads

13. 1.13 User level threads vs. kernel threads

14. 1.14 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. 1.15 First-Come, First-Served (FCFS) Scheduling ProcessBurst Time P 1 24 P 2 3 P 3 3 Suppose that the processes arrive in the order: P 1, P 2, P 3 The Gantt Chart for the schedule is: Waiting time for P 1 = 0; P 2 = 24; P 3 = 27 Average waiting time: (0 + 24 + 27)/3 = 17 P1P1 P2P2 P3P3 2427300

16. 1.16 Multilevel Feedback Queues

17. 1.17 CPU Scheduling Multiprocessor Scheduling Processor affinity vs. load balancing Evaluation of Algorithms Modeling, simulation, implementation

18. 1.18 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: Peterson’s Algorithm Hardware support: TestAndSet(), Swap()  Busy waiting (or spinlocks) Semaphores:  Not busy waiting  wait(), signal() must be atomic  moves the CS problem to kernel Monitors  High-level (programming language) constructs

19. 1.19 Synchronization Some classical synchronization problems Consumer-producer Dining philosopher Readers-writers

20. 1.20 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 {P 0, P 1, …, P 0 } of waiting processes such that P 0 is waiting for a resource that is held by P 1, P 1 is waiting for a resource that is held by P 2, …, P n–1 is waiting for a resource that is held by P n, and P 0 is waiting for a resource that is held by P 0

21. 1.21 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 Banker’s algorithm: multiple instances of a resource type Detection and Recovery Detection algorithm Recovery: process termination or resource preemption

22. 1.22 Good Luck on the Exam!