Module 1 OS PDF

MODULE 1: Introduction Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009  Unit I -Basic of Operating System and Its Structures Introduction to Operating System Computer System Organization Architecture- Structure-Operations. Manag...

MODULE 1: Introduction Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009  Unit I -Basic of Operating System and Its Structures Introduction to Operating System Computer System Organization Architecture- Structure-Operations. Management:Process-Memory-Storage. Structures:Services-System Interface System Calls System Program Design-structure Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009  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 Operating System Concepts – 8th Edition 3 Silberschatz, Galvin and Gagne ©2009  Objectives To provide a grand tour of the major operating systems components To provide coverage of basic computer system organization Operating System Concepts – 8th Edition 4 Silberschatz, Galvin and Gagne ©2009  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 Operating System Concepts – 8th Edition 5 Silberschatz, Galvin and Gagne ©2009     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 Operating System Concepts – 8th Edition 6 Silberschatz, Galvin and Gagne ©2009      Four Components of a Computer System Operating System Concepts – 8th Edition 7 Silberschatz, Galvin and Gagne ©2009  What Operating Systems Do Depends on the point of view Users want convenience, ease of use 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 Operating System Concepts – 8th Edition 8 Silberschatz, Galvin and Gagne ©2009   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 Operating System Concepts – 8th Edition 9 Silberschatz, Galvin and Gagne ©2009     Operating System Definition (Cont.) No universally accepted definition “Everything a vendor ships when you order an operating system” is 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. Operating System Concepts – 8th Edition 10 Silberschatz, Galvin and Gagne ©2009   Kernel in Operating System Operating System Concepts – 8th Edition 11 Silberschatz, Galvin and Gagne ©2009  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 * EPROM stands for Erasable Programmable ROM, it is non-volatile memory chip that can hold the data even if the power supply is stopped. This can be read and written optically. EPROM may be re-programmed whereas PROM cannot. Operating System Concepts – 8th Edition 12 Silberschatz, Galvin and Gagne ©2009      Computer System Organisation Computer-system operation One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles Operating System Concepts – 8th Edition 13 Silberschatz, Galvin and Gagne ©2009    Computer-System Operation I/O devices and the CPU can execute concurrently Each device controller is in charge of a particular device type Each device controller has a local buffer CPU moves data from/to main memory to/from local buffers I/O is from the device to local buffer of controller Device controller informs CPU that it has finished its operation by causing an interrupt Operating System Concepts – 8th Edition 14 Silberschatz, Galvin and Gagne ©2009  Common Functions of Interrupts Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines Interrupt architecture must save the address of the interrupted instruction Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt A trap is a software-generated interrupt caused either by an error or a user request An operating system is interrupt driven Operating System Concepts – 8th Edition 15 Silberschatz, Galvin and Gagne ©2009  Interrupt Handling The operating system preserves the state of the CPU by storing registers and the program counter Determines which type of interrupt has occurred: Polling- multiple interrupt sources share the same interrupt vector address vectored interrupt system- each interrupt vector source has a unique interrupt vector address Separate segments of code determine what action should be taken for each type of interrupt Operating System Concepts – 8th Edition 16 Silberschatz, Galvin and Gagne ©2009    I/O Structure After I/O starts, control returns to user program only upon I/O completion Wait instruction idles the CPU until the next interrupt Wait loop (contention for memory access) At most one I/O request is outstanding at a time, no simultaneous I/ O processing After I/O starts, control returns to user program without waiting for I/O completion 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 Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt Operating System Concepts – 8th Edition 17 Silberschatz, Galvin and Gagne ©2009        Direct Memory Access Structure Used for high-speed I/O devices able to transmit information at close to memory speeds Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention Operating System Concepts – 8th Edition 18 Silberschatz, Galvin and Gagne ©2009  Storage Structure Main memory – only large storage media that the CPU can access directly Random access Typically volatile (memory that keep the information only the time it is powered up) Secondary storage – extension of main memory that provides large nonvolatile storage capacity Magnetic disks – rigid metal or glass platters covered with magnetic recording material Disk surface is logically divided into tracks, which are subdivided into sectors The disk controller determines the logical interaction between the device and the computer Operating System Concepts – 8th Edition 19 Silberschatz, Galvin and Gagne ©2009      Storage Hierarchy Storage systems organized in hierarchy Speed Cost Volatility Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage Operating System Concepts – 8th Edition 20 Silberschatz, Galvin and Gagne ©2009     Storage-Device Hierarchy Used for operating systems, application Secondary programs and data storage storage Used for archiving and media distribution Used for electronic data storage Operating System Concepts – 8th Edition 21 Silberschatz, Galvin and Gagne ©2009  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 Operating System Concepts – 8th Edition 22 Silberschatz, Galvin and Gagne ©2009      Computer-System Architecture Most systems use a single general-purpose processor (PDAs through mainframes) Most systems have special-purpose processors as well Multiprocessors systems growing in use and importance Also known as parallel systems, tightly-coupled systems Advantages include: 1. Increased throughput 2. Economy of scale 3. Increased reliability – graceful degradation or fault tolerance Two types: 1. Asymmetric Multiprocessing 2. Symmetric Multiprocessing Operating System Concepts – 8th Edition 23 Silberschatz, Galvin and Gagne ©2009      How a Modern Computer Works A von Neumann architecture Operating System Concepts – 8th Edition 24 Silberschatz, Galvin and Gagne ©2009  Symmetric Multiprocessing Architecture Operating System Concepts – 8th Edition 25 Silberschatz, Galvin and Gagne ©2009  A Dual-Core Design Operating System Concepts – 8th Edition 26 Silberschatz, Galvin and Gagne ©2009  Clustered Systems Like multiprocessor systems, but multiple systems working together Usually sharing storage via a storage-area network (SAN) Provides a high-availability service which survives failures  Asymmetric clustering has one machine in hot-standby mode  Symmetric clustering has multiple nodes running applications, monitoring each other Some clusters are for high-performance computing (HPC)  Applications must be written to use parallelization Operating System Concepts – 8th Edition 27 Silberschatz, Galvin and Gagne ©2009     Clustered Systems Operating System Concepts – 8th Edition 28 Silberschatz, Galvin and Gagne ©2009  Operating System Structure Multiprogramming 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 Operating System Concepts – 8th Edition 29 Silberschatz, Galvin and Gagne ©2009            Memory Layout for Multiprogrammed System Operating System Concepts – 8th Edition 30 Silberschatz, Galvin and Gagne ©2009  Operating-System Operations Interrupt driven by hardware Software error or request creates exception or trap Division by zero, request for operating system service Other process problems include infinite loop, processes modifying each other or the operating system 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 Operating System Concepts – 8th Edition 31 Silberschatz, Galvin and Gagne ©2009     Transition from User to Kernel Mode Timer to prevent infinite loop / process hogging resources Set interrupt after specific period Operating system decrements counter When counter zero generate an interrupt Set up before scheduling process to regain control or terminate program that exceeds allotted time Operating System Concepts – 8th Edition 32 Silberschatz, Galvin and Gagne ©2009      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 Operating System Concepts – 8th Edition 33 Silberschatz, Galvin and Gagne ©2009      Process Management Activities The operating system is responsible for the following activities in connection with process management: 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 Operating System Concepts – 8th Edition 34 Silberschatz, Galvin and Gagne ©2009  Memory Management All data in memory before and after processing All instructions in memory in order to execute Memory management determines what is in memory 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 Operating System Concepts – 8th Edition 35 Silberschatz, Galvin and Gagne ©2009      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 dirs  Mapping files onto secondary storage  Backup files onto stable (non-volatile) storage media Operating System Concepts – 8th Edition 36 Silberschatz, Galvin and Gagne ©2009       Mass-Storage Management Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time Proper management is of central importance Entire speed of computer operation hinges on disk subsystem and its algorithms OS activities Free-space management Storage allocation Disk scheduling Some storage need not be fast Tertiary storage includes optical storage, magnetic tape Still must be managed – by OS or applications Varies between WORM (write-once, read-many-times) and RW (read-write) Operating System Concepts – 8th Edition 37 Silberschatz, Galvin and Gagne ©2009        Performance of Various Levels of Storage Movement between levels of storage hierarchy can be explicit or implicit Operating System Concepts – 8th Edition 38 Silberschatz, Galvin and Gagne ©2009  Migration of Integer A from Disk to Register Multitasking environments must be careful to use most recent value, no matter where it is stored in the storage hierarchy Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache Distributed environment situation even more complex Several copies of a datum can exist Various solutions covered in Chapter 17 Operating System Concepts – 8th Edition 39 Silberschatz, Galvin and Gagne ©2009    I/O Subsystem One purpose of OS is to hide peculiarities of hardware devices from the user I/O subsystem responsible for Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs) General device-driver interface Drivers for specific hardware devices Operating System Concepts – 8th Edition 40 Silberschatz, Galvin and Gagne ©2009     Protection and Security Protection – any mechanism for controlling access of processes or users to resources defined by the OS Security – defense of the system against internal and external attacks Huge range, including denial-of-service, worms, viruses, identity theft, theft of service Systems generally first distinguish among users, to determine who can do what User identities (user IDs, security IDs) include name and associated number, one per user User ID then associated with all files, processes of that user to determine access control Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file Privilege escalation allows user to change to effective ID with more rights Operating System Concepts – 8th Edition 41 Silberschatz, Galvin and Gagne ©2009       End of Chapter 1 Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009