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Study Guide to Accompany Operating Systems Concepts 9th Ed by Silberschatz, Gal

Study Guide to Accompany Operating Systems Concepts 9th Ed by Silberschatz, Galvin and Gagne By Andrew DeNicola, BU ECE Class of 2012 Figures Copyright © John Wiley & Sons 2012 Ch.1 - Introduction  An OS isa program that acts as an intermediary between a user of a computer and the computer hardware  Goals: Execute user programs, make the comp. system easy to use, utilize hardware efficiently  Computer system: Hardware ↔ OS ↔ Applications ↔ Users (↔ = 'uses')  OS is: ◦ Resource allocator: decides between conflicting requests for efficient and fair resource use ◦ Control program: controls execution of programs to prevent errors and improper use of computer  Kernel: the one program running at all times on the computer  Bootstrap program: loaded at power-up or reboot ◦ Stored in ROM or EPROM (known as firmware), Initializes all aspects of system, loads OS kernel and starts execution  I/O and CPU can execute concurrently  Device controllers inform CPU that it is finished w/ operation by causing an interrupt ◦ Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines ◦ Incoming interrupts are disabled while another interrupt is being processed ◦ Trap is a software generated interrupt caused by error or user request ◦ OS determines which type of interrupt has occurred by polling or the vectored interrupt system  System call: request to the operating system to allow user to wait for I/O completion  Device-status table:contains entry for each I/O device indicating its type, address, and state ◦ OS indexes into the I/O device table to determine device status and to modify the table entry to include interrupt  Storage structure: ◦ Main memory – random access, volatile ◦ Secondary storage – extension of main memory That provides large non-volatile storage ◦ Disk – divided into tracks which are subdivided into sectors. Disk controller determines logical interaction between the device and the computer.  Caching – copying information into faster storage system  Multiprocessor Systems:Increased throughput, economy of scale, increased reliability ◦ Can be asymmetric or symmetric ◦ Clustered systems – Linked multiprocessor systems  Multiprogramming – Provides efficiency via job scheduling ◦ When OS has to wait (ex: for I/O), switches to another job  Timesharing – CPU switches jobs so frequently that each user can interact with each job while it is running (interactive computing)  Dual-mode operation allows OS to protect itself and other system components – User mode and kernel mode ◦ Some instructions are only executable in kernel mode, these are privileged  Single-threaded processes have one program counter, multi-threaded processes have one PC per thread  Protection – mechanism for controlling access of processes or users to resources defined by the OS  Security – defense of a system against attacks  User IDs (UID), one per user, and Group IDs, determine which users and groups of users have which privileges Ch.2 – OS Structures  User Interface (UI) – Can be Command-Line (CLI) or Graphics User Interface (GUI) or Batch ◦ These allow for the user to interact with the system services via system calls (typically written in C/C++)  Other system services that a helpful to the user include: program execution, I/O operations, file-system manipulation, communications, and error detection  Services that exist to ensure efficient OS operation are: resource allocation, accounting, protection and security  Most system calls are accessed by Application Program Interface (API) such as Win32, POSIX, Java  Usually there is a number associated with each system call ◦ System call interface maintains a table indexed according to these numbers  Parameters may need to be passed to the OS during a system call, may be done by: ◦ Passing in registers, address of parameter stored in a block, pushed onto the stack by the program and popped off by the OS ◦ Block and stack methods do not limit the number or length of parameters being passed  Process control system calls include: end, abort, load, execute, create/terminate process, wait, allocate/free memory  File management system calls include: create/delete file, open/close file, read, write, get/set attributes  Device management system calls: request/release device, read, write, logically attach/detach devices  Information maintenance system calls: get/set time, get/set system data, get/set process/file/device attributes  Communications system calls: create/delete communication connection, send/receive, transfer status information  OS Layered approach: ◦ The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface ◦ With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers  Virtual machine: uses layered approach, treats hardware and the OS kernel as though they were all hardware. ◦ Host creates the illusion that a process has its own processor and own virtual memory ◦ Each guest provided with a 'virtual' copy of the underlying computer  Application failures can generate core dump file capturing memory of the process  Operating system failure can generate crash dump file containing kernel memory Ch.3 – Processes  Process contains a program counter, stack, and data section. ◦ Text section: program code itself ◦ Stack: temporary data (function parameters, return addresses, local variables) ◦ Data section: global variables ◦ Heap: contains memory dynamically allocated during run-time  Process Control Block (PCB): contains information associated with each process: process state, PC, CPU registers, scheduling information, accounting information, I/O status information  Types of processes: ◦ I/O Bound: spends more time doing I/O than computations, many short CPU bursts ◦ CPU Bound: spends more time doing computations, few very long CPU bursts  When CPU switches to another process, the system must save the state of the old process (to PCB) and load the saved state (from PCB) for the new process via a context switch ◦ Time of a context switch is dependent on hardware  Parent processes create children processes (form a tree) ◦ PID allows for process management ◦ Parents and children can share all/some/none resources ◦ Parents can execute concurrently with children or wait until children terminate ◦ fork() system call creates new process ▪ exec() system call used after a fork to replace the processes' memory space with a new program  Cooperating processes need interprocess communication (IPC): shared memory or message passing  Message passing may be blocking or non-blocking ◦ Blocking is considered synchronous ▪ Blocking send has the sender block until the message is received ▪ Blocking receive has the receiver block until a message is available ◦ Non-blocking is considered asynchronous ▪ Non-blocking send has the sender send the message and continue ▪ Non-blocking receive has the receiver receive a valid message or null Ch.4 – Threads  Threads are fundamental unit of CPU utilization that forms the basis of multi-threaded computer systems  Process creation is heavy-weight while thread creation is light-weight ◦ Can simplify code and increase efficiency  Kernels are generally multi-threaded  Multi-threading models include: Many-to-One, One-to-One, Many-to-Many ◦ Many-to-One: Many user-level threads mapped to single kernel thread ◦ One-to-One: Each user-level thread maps to kernel thread ◦ Many-to-Many: Many user-level threads mapped to many kernel threads  Thread library provides programmer with API for creating and managing threads  Issues include: thread cancellation, signal handling (synchronous/asynchronous), handling thread-specific data, and scheduler activations. ◦ Cancellation: ▪ Asynchronous cancellation terminates the target thread immediately ▪ Deferred cancellation allows the target thread to periodically check if it should be canceled ◦ Signal handler processes signals generated by a particular event, delivered to a process, handled ◦ Scheduler activations provide upcalls – a communication mechanism from the kernel to the thread library. ▪ Allows application to maintain the correct number of kernel threads Ch.5 – Process Synchronization  Race Condition: several processes access and manipulate the same data concurrently, outcome depends on which order each access takes place.  Each process has critical section of code, where it is manipulating data ◦ To solve critical section problem each process must ask permission to enter critical section in entry section, follow critical section with exit section and then execute the remainder section ◦ Especially difficult to solve this problem in preemptive kernels  Peterson's Solution: solution for two processes ◦ Two processes share two variables: int turn and Boolean flag[2] ◦ turn: whose turn it is to enter the critical section ◦ flag: indication of whether or not a process is ready to enter critical section ▪ flag[i] = true indicates that process Pi is ready ◦ Algorithm for process Pi: do { flag[i] = TRUE; turn = j; while (flag[j] && turn == j) critical section flag[i] = FALSE; remainder section } while (TRUE);  Modern machines provide atomic hardware instructions: Atomic = non-interruptable  Solution using Locks: do { acquire lock critical section release lock remainder section } while (TRUE);  Solution uploads/Management/ study-guide 15 .pdf