Chapter 1: Introduction

1.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Outline n What Operating Systems Do n Computer-System Organization n Computer-System Architecture n Operating-System Structure n Operating-System Operations n Process Management n Memory Management n Storage Management n Protection and Security n Distributed Systems n Special-Purpose Systems n Computing Environments

1.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Objectives n To provide a grand tour of the major operating systems components n To provide coverage of basic computer system organization

1.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 What is an Operating System? n A program between computer users and computer hardware l To manage and use computer hardware in an efficient manner n Operating system goals: l To provide an environment for users to execute programs in a convenient and efficient manner l To ensure the correct operation of the computer system

1.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Computer System Structure n Four components Hardware – basic computing resources  CPU, memory, I/O devices l 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 l Users  People, machines, other computers

1.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Four Components of a Computer System

1.7 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Operating System Definition n OS is a resource allocator l Manages all resources l Decides between conflicting requests for efficient and fair resource use n OS is a control program l Controls execution of programs to prevent errors and improper use of the computer

1.8 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Operating System Definition (Cont.) n No universally accepted definition “ Everything a vendor ships when you order an operating system ” is good approximation l But varies wildly “ The one program running at all times on the computer ” is the kernel l Everything else is either a system program or an application program

1.9 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Computer Startup n bootstrap program is loaded at power-up or reboot l Typically stored in ROM or EPROM, generally known as firmware l Initializates all aspects of system l Loads OS kernel and starts execution

1.10 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Computer System Organization n One or more CPUs, device controllers connect through common bus providing access to shared memory n Concurrent execution of CPUs and devices competing for memory cycles

1.11 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Computer-System Operation n I/O devices and CPU can execute concurrently l Each device controller is in charge of a device type l Each device controller has a local buffer n I/O operations l I/O is from the device to the local buffer l Device controller informs CPU by causing an interrupt l CPU moves data between local buffers and main memory

1.12 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Common Functions of Interrupts n Interrupt transfers control to the interrupt service routine l through interrupt vector, which contains the addresses of all the service routines n Interrupt architecture must save the address of the interrupted instruction n Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt n A trap is a software-generated interrupt caused either by an error or a user request n An interrupt driven OS

1.13 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Interrupt Timeline

1.14 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 I/O Structure n Syncrhonous: After I/O starts, control returns to user program only upon I/O completion l Wait instruction idles the CPU until the next interrupt l Wait loop (contention for memory access) l At most one I/O request at a time, no simultaneous I/O processing n Asynchronous: After I/O starts, control returns to user program without waiting for I/O completion System call – request to the OS to allow user to wait for I/O completion l Device-status table for each I/O device: type, address, and state l OS indexes into I/O device table to determine device status and to modify table entry to include interrupt

1.15 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Direct Memory Access Structure n Used for high-speed I/O devices l able to transmit information at close to memory speeds n Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention n Only one interrupt is generated per block, rather than the one interrupt per byte

1.16 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Storage Structure Main memory – the only large storage media that the CPU can access directly 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.

1.17 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Storage Hierarchy n Storage systems organized in hierarchy. l Speed l Cost l Volatility Caching – copying information into faster storage system l main memory as a last cache for secondary storage

1.18 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Storage-Device Hierarchy

1.19 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 How a Modern Computer Works

1.20 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Computer-System Architecture n Single processor systems l general-purpose and special-purpose processors n Multiprocessor systems growing in use and importance l Also known as parallel systems, tightly-coupled systems l Advantages include 1. Increased throughput 2. Economy of scale 3. Increased reliability – graceful degradation or fault tolerance l Two types 1. Asymmetric Multiprocessing 2. Symmetric Multiprocessing (SMP)

1.21 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Symmetric Multiprocessing Architecture

1.22 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 A Dual-Core Design

1.23 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Clustered Systems n Like multiprocessor systems, but multiple systems working together l Usually sharing storage via a storage-area network (SAN) l 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 l Some clusters are for high-performance computing (HPC)  Applications must be written to use parallelization

1.24 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Operating System Structure n Multiprogramming needed for efficiency l Single user cannot keep CPU and I/O devices busy at all times l Multiprogramming organizes jobs so CPU always has one to execute l A subset of total jobs in system is kept in memory l One job selected and run via job scheduling l When it has to wait (for I/O for example), OS switches to another job

1.25 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 n Timesharing (multitasking): a logical extension l CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing l Response time should be < 1 second l Each user has at least one program executing in memory  process l 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 l Virtual memory allows execution of processes not completely in memory

1.26 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Memory Layout for Multiprogrammed System

1.27 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Operating-System Operations n Interrupt driven by hardware n Software error or request creates exception or trap l Division by zero, request for OS service l Other process problems include infinite loop, processes modifying each other or the OS

1.28 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 n Dual-mode operation allows OS to protect itself and other components l User mode and kernel mode l 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

1.29 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Transition from User to Kernel Mode n Timer to prevent infinite loop / process hogging resources l Set interrupt after specific period l OS decrements counter l When counter zero generate an interrupt l Set up before scheduling process to regain control or terminate program that exceeds allotted time

1.30 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Process Management n A process ( active ) is a program ( passive ) in execution l Process needs resources to accomplish its task  CPU, memory, I/O, files l Process termination requires reclaim of any reusable resources n Single-threaded process has one program counter specifying location of next instruction to execute n Multi-threaded process has one program counter per thread l Many processes running concurrently by multiplexing the CPUs among the processes / threads

1.31 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Process Management Activities Process management activities: (Chap. 3-6) n Creating and deleting both user and system processes n Suspending and resuming processes n Providing mechanisms for process synchronization n Providing mechanisms for process communication n Providing mechanisms for deadlock handling

1.32 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Memory Management n All data in memory before and after processing n All instructions in memory in order to execute n Memory management determines what is in memory when l Optimizing CPU utilization and computer response to users n Memory management activities (Chap. 8-9) l Keeping track of which parts of memory are currently being used and by whom l Deciding which processes and data to move into and out of memory l Allocating and deallocating memory space as needed

1.33 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Storage Management n OS provides uniform, logical view of information storage l Abstracts physical properties to logical storage unit - file l Each medium is controlled by device (i.e., disk, tape drive)  Varying properties include access speed, capacity, data- transfer rate, access method (sequential or random)

1.34 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 File-System Management n File-System management l Files usually organized into directories l Access control on most systems to determine who can access what l File management activities: (Chap )  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

1.35 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 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 l Proper management is of central importance l Bottleneck of the whole system n Disk management activities: (Chap. 12) l Free-space management l Storage allocation l Disk scheduling n Some storage need not be fast l Tertiary storage includes optical storage, magnetic tape  Varies between WORM (write-once, read-many- times) and RW (read-write)

1.36 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Caching n Important principle, performed at many levels in a computer (in hardware, operating system, software) n Information in use copied from slower to faster storage temporarily n Faster storage (cache) checked first to determine if information is there l If it is, information used directly from the cache (fast) l If not, data copied to cache and used there n Cache smaller than storage being cached l Cache management important design problem l Cache size and replacement policy

1.37 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Performance of Various Levels of Storage n Movement between levels of storage hierarchy can be explicit or implicit

1.38 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Migration of Integer A from Disk to Register n Multitasking environments must be careful to use most recent value, no matter where it is stored in the storage hierarchy n Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache n Distributed environment situation even more complex l Several copies of a datum can exist (Chap. 17)

1.39 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 I/O Subsystem n To hide peculiarities of hardware devices from the user n I/O subsystem components: (Chap. 13) l 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) l General device-driver interface l Drivers for specific hardware devices

1.40 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Protection and Security Protection – any mechanism for controlling access of processes or users to resources (Chap. 17) Security – defense of the system against internal and external attacks (Chap. 18) l Huge range, including denial-of-service, worms, viruses, identity theft, theft of service n Systems generally first distinguish among users, to determine who can do what l User identities ( user IDs, security IDs): name and associated number, one per user l Group identifier (g roup ID ): set of users  User ID, group ID then associated with all files, processes of that user to determine access control l Privilege escalation allows user to change to effective ID with more rights

1.41 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Computing Environments n Traditional computer l Blurring over time l Office environment  PCs connected to a network, terminals attached to mainframe or minicomputers providing batch and timesharing  Now portals allowing networked and remote systems access to same resources l Home networks  Used to be single system, then modems  Now firewalled, networked

1.42 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Computing Environments (Cont.) n Client-Server Computing l Many systems now servers, responding to requests generated by clients  Compute-server provides an interface for clients to request services (i.e. database)  File-server provides interface for clients to store and retrieve files

1.43 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Peer-to-Peer Computing n Another model of distributed system n P2P does not distinguish clients and servers l All nodes are considered peers  May each act as client, server or both l Node must join P2P network  Registers its service with central lookup service on network, or  Broadcast request for service and respond to requests for service via discovery protocol l Examples include Napster and Gnutella

1.44 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Web-Based Computing n Web has become ubiquitous l PCs most prevalent devices l More devices becoming networked to allow web access n New category of devices to manage web traffic among similar servers: load balancers n Use of operating systems like Windows 95, web clients, have evolved into Linux and Windows XP, which can be clients and servers

1.45 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Jan 12, 2005 Open-Source Operating Systems n Operating systems made available in source-code format rather than just binary closed-source n Counter to the copy protection and Digital Rights Management (DRM) movement n Started by Free Software Foundation (FSF), which has “copyleft” GNU Public License (GPL) n Examples include GNU/Linux, BSD UNIX (including core of Mac OS X), and Sun Solaris

End of Chapter 1