introduction to operating systems and services.pptx
- 1. Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edit9on Chapter 1: Introduction
- 2. Chapter 1: Introduction • What Operating Systems Do • Computer-System Organization • Computer-System Architecture • Operating-System Structure • Operating-System Operations • Process Management • Memory Management • Storage Management • Protection and Security • Kernel Data Structures • Computing Environments • Open-Source Operating Systems
- 3. Objectives • To describe the basic organization of computer systems • To provide a grand tour of the major components of operating systems • To give an overview of the many types of computing environments • To explore several open-source operating systems
- 4. What is an Operating System? • A program that acts as an intermediary between a user of a computer and the computer hardware • Operating system goals: • Execute user programs and make solving user problems easier • Make the computer system convenient to use • Use the computer hardware in an efficient manner
- 5. Computer System Structure • Computer system can be divided into four components: • Hardware – provides basic computing resources • CPU, memory, I/O devices • Operating system • Controls and coordinates use of hardware among various applications and users • Application programs – define the ways in which the system resources are used to solve the computing problems of the users • Word processors, compilers, web browsers, database systems, video games • Users • People, machines, other computers
- 6. Four Components of a Computer System
- 7. What Operating Systems Do • Depends on the point of view • Users want convenience, ease of use and good performance • Don’t care about resource utilization • But shared computer such as mainframe or minicomputer must keep all users happy • Users of dedicate systems such as workstations have dedicated resources but frequently use shared resources from servers • Handheld computers are resource poor, optimized for usability and battery life • Some computers have little or no user interface, such as embedded computers in devices and automobiles
- 8. Operating System Definition • OS is a resource allocator • Manages all resources • Decides between conflicting requests for efficient and fair resource use • OS is a control program • Controls execution of programs to prevent errors and improper use of the computer
- 9. Operating System Definition (Cont.) • No universally accepted definition • “Everything a vendor ships when you order an operating system” is a good approximation • But varies wildly • “The one program running at all times on the computer” is the kernel. • Everything else is either • a system program (ships with the operating system) , or • an application program.
- 10. Computer Startup • bootstrap program is loaded at power-up or reboot • Typically stored in ROM or EPROM, generally known as firmware • Initializes all aspects of system • Loads operating system kernel and starts execution
- 12. Caching • Important principle, performed at many levels in a computer (in hardware, operating system, software) • Information in use copied from slower to faster storage temporarily • Faster storage (cache) checked first to determine if information is there • If it is, information used directly from the cache (fast) • If not, data copied to cache and used there • Cache smaller than storage being cached • Cache management important design problem • Cache size and replacement policy
- 13. Operating System Structure • Multiprogramming (Batch system) needed for efficiency • Single user cannot keep CPU and I/O devices busy at all times • Multiprogramming organizes jobs (code and data) so CPU always has one to execute • A subset of total jobs in system is kept in memory • One job selected and run via job scheduling • When it has to wait (for I/O for example), OS switches to another job • Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing • Response time should be < 1 second • Each user has at least one program executing in memory process • If several jobs ready to run at the same time CPU scheduling • If processes don’t fit in memory, swapping moves them in and out to run • Virtual memory allows execution of processes not completely in memory
- 14. Memory Layout for Multiprogrammed System
- 15. Operating-System Operations • Interrupt driven (hardware and software) • Hardware interrupt by one of the devices • Software interrupt (exception or trap): • Software error (e.g., division by zero) • Request for operating system service • Other process problems include infinite loop, processes modifying each other or the operating system
- 16. Operating-System Operations (cont.) • 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 • Increasingly CPUs support multi-mode operations • i.e. virtual machine manager (VMM) mode for guest VMs
- 17. Transition from User to Kernel Mode • Timer to prevent infinite loop / process hogging resources • Timer is set to interrupt the computer after some time period • Keep a counter that is decremented by the physical clock. • Operating system set the counter (privileged instruction) • When counter zero generate an interrupt • Set up before scheduling process to regain control or terminate program that exceeds allotted time
- 18. Process Management • A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity. • Process needs resources to accomplish its task • CPU, memory, I/O, files • Initialization data • Process termination requires reclaim of any reusable resources • Single-threaded process has one program counter specifying location of next instruction to execute • Process executes instructions sequentially, one at a time, until completion • Multi-threaded process has one program counter per thread • Typically system has many processes, some user, some operating system running concurrently on one or more CPUs • Concurrency by multiplexing the CPUs among the processes / threads
- 19. Process Management Activities • Creating and deleting both user and system processes • Suspending and resuming processes • Providing mechanisms for process synchronization • Providing mechanisms for process communication • Providing mechanisms for deadlock handling The operating system is responsible for the following activities in connection with process management:
- 20. Memory Management • To execute a program all (or part) of the instructions must be in memory • All (or part) of the data that is needed by the program must be in memory. • Memory management determines what is in memory and when • Optimizing CPU utilization and computer response to users • Memory management activities • Keeping track of which parts of memory are currently being used and by whom • Deciding which processes (or parts thereof) and data to move into and out of memory • Allocating and deallocating memory space as needed
- 21. Storage Management • OS provides uniform, logical view of information storage • Abstracts physical properties to logical storage unit - file • Each medium is controlled by device (i.e., disk drive, tape drive) • Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random) • File-System management • Files usually organized into directories • Access control on most systems to determine who can access what • OS activities include • Creating and deleting files and directories • Primitives to manipulate files and directories • Mapping files onto secondary storage • Backup files onto stable (non-volatile) storage media
- 22. Kernel Data Structures Many similar to standard programming data structures Singly linked list Doubly linked list Circular linked list
- 23. Kernel Data Structures • Binary search tree left <= right • Search performance is O(n) • Balanced binary search tree is O(lg n)
- 24. Kernel Data Structures • Hash function can create a hash map • Bitmap – string of n binary digits representing the status of n items • Linux data structures defined in include files <linux/list.h>, <linux/kfifo.h>, <linux/rbtree.h>
- 25. Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edit9on End of Chapter 1