3 Wiley Asia Student Edition 課程計畫 (2/2)Wiley Asia Student Edition實施方法：課堂講述、作業練習、定期考試評量方式：作業60%、考試30%、上課參與10%。上課用書：Silberschatz, A., Galvin, P. B., & Gagne, G. (2006). ASE Operating System principles (7th Ed.). USA: John Wiley & Sons.
4 Chapter 1: Introduction What Operating Systems DoComputer-System OrganizationComputer-System ArchitectureOperating-System StructureOperating-System OperationsProcess ManagementMemory ManagementStorage ManagementProtection and SecurityDistributed SystemsSpecial-Purpose SystemsComputing Environments
5 1.1 What Operating System Do? What is an Operating System?A program that manages the computer hardware and acts as an intermediary between a user of a computer and the computer hardware.An operating system is similar to a government. It simply provides an environment within which other programs can do useful work.
6 Four Components of a Computer System (2/4) People, machines, other computersdefine the ways in which the system resources are used to solve the computing problems of the usersControls and coordinates use of hardware among various applications and usersprovides basic computing resources: CPU, memory, I/O devicesFig. 1.1
7 What is an Operating System? User View:Ease of useMaximize resource utilizationCompromise between individual usability and resource utilization
8 What is an Operating System? System View:OS is a resource allocatorManages all resourcesDecides between conflicting requests for efficient and fair resource useOS is a control programControls execution of programs to prevent errors and improper use of the computer
9 Operating System Definition (1/2) 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 (Fig. 1.1)The common functions of controlling and allocation resources
10 Operating System Definition (2/2) No universally accepted definition“Everything a vendor ships when you order an operating system” is good approximationBut varies wildly“The one program running at all times on the computer” is the kernel. Everything else is either a system program or an application program
11 1.2 Computer System Organization Computer-system operationOne or more CPUs, device controllers connect through common bus providing access to shared memoryConcurrent execution of CPUs and devices competing for memory cyclesFig. A modern computer system.
12 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 buffersI/O is from the device to local buffer of controller.Device controller informs CPU that it has finished its operation by causing an interrupt.
13 I/O StructureAfter I/O starts, control returns to user program only upon I/O completion.Wait instruction idles the CPU until the next interruptWait 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.
14 Fig. 1.3 Interrupt time line for a single process doing output.
15 Storage StructureMain memory – 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 materialDisk surface is logically divided into tracks, which are subdivided into sectors.The disk controller determines the logical interaction between the device and the computer.Storage systems organized in hierarchy.SpeedCostVolatility
17 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.Only on interrupt is generated per block, rather than the one interrupt per byte.
18 1.3 Computer-System Architecture Single-Processor SystemsMultiprocessor SystemsClustered Systems
19 Single-Processor Systems There is one main CPU capable of executing a general-purpose instruction set, including instructions from user processes.
20 Multiprocessor Systems (1/2) two or more processors in close communication, sharing the computer bus and sometimes the clock, memory, and peripheral devicesAdvantagesIncrease throughputEconomy of scaleIncrease reliability: graceful degradation, fault tolerant
21 Multiprocessor Systems (2/2) Asymmetric multiprocessing (master-slave relationship): A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks.Symmetric multiprocessing (SMP): each processor performs all tasks within the operating system. (Windows XP, Mac OS, Linux)memoryFig. 1.6 SMP architecture
22 Clustered SystemsClustered computers share storage and are closely linked via a local-area network (LAN) or wide-area network (parallel clusters)Provide high-availability serviceAsymmetric clustering vs. symmetric modeAsymmetric clustering: one machine is in hot-standby mode while the other is running the applications. The hot-standby host machine does nothing but monitor the active server. If that server fails, the hot-standby host becomes the active server.Symmetric clustering: two or more hosts are running applications, and are monitoring each other.
23 1.4 Operating System Structure Multiprogramming needed for efficiencySingle user cannot keep CPU and I/O devices busy at all timesMultiprogramming organizes jobs (code and data) so CPU always has one to executeA subset of total jobs in system is kept in memoryOne job selected and run via job schedulingWhen it has to wait (for I/O for example), OS switches to another jobMemory Layout for Multiprogrammed System
24 1.4 Operating System Structure 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 computingResponse time should be < 1 secondEach user has at least one program executing in memory processIf several jobs ready to run at the same time CPU schedulingIf processes don’t fit in memory, swapping moves them in and out to runVirtual memory allows execution of processes not completely in memory
25 1.5 Operating-System Operations Interrupt driven by hardwareSoftware error or request creates exception or trapDivision by zero, request for operating system serviceOther process problems include infinite loop, processes modifying each other or the operating systemDual-mode operation allows OS to protect itself and other system componentsUser mode and kernel modeMode bit provided by hardwareProvides ability to distinguish when system is running user code or kernel codeSome instructions designated as privileged, only executable in kernel modeSystem call changes mode to kernel, return from call resets it to user
26 1.5 Operating-System Operations Fig. 1.8 Transition from user to kernel mode.
27 Timer Timer to prevent infinite loop / process hogging resources Set interrupt after specific periodOperating system decrements counterWhen counter zero generate an interruptSet up before scheduling process to regain control or terminate program that exceeds allotted time
28 1.6 Process ManagementA 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 taskCPU, memory, I/O, filesInitialization dataProcess termination requires reclaim of any reusable resourcesSingle-threaded process has one program counter specifying location of next instruction to executeProcess executes instructions sequentially, one at a time, until completionMulti-threaded process has one program counter per threadTypically system has many processes, some user, some operating system running concurrently on one or more CPUsConcurrency by multiplexing the CPUs among the processes / threads
29 Process Management Activities The operating system is responsible for the following activities in connection with process management:Creating and deleting both user and system processesSuspending and resuming processesProviding mechanisms for process synchronizationProviding mechanisms for process communicationProviding mechanisms for deadlock handling
30 1.7 Memory Management All data in memory before and after processing All instructions in memory in order to executeMemory management determines what is in memory whenOptimizing CPU utilization and computer response to usersMemory management activitiesKeeping track of which parts of memory are currently being used and by whomDeciding which processes (or parts thereof) and data to move into and out of memoryAllocating and deallocating memory space as needed
31 1.8 Storage ManagementOS provides uniform, logical view of information storageAbstracts physical properties to logical storage unit - fileEach 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 managementFiles usually organized into directoriesAccess control on most systems to determine who can access whatOS activities includeCreating and deleting files and directoriesPrimitives to manipulate files and dirsMapping files onto secondary storageBackup files onto stable (non-volatile) storage media
32 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 importanceEntire speed of computer operation hinges on disk subsystem and its algorithmsOS activitiesFree-space managementStorage allocationDisk schedulingSome storage need not be fastTertiary storage includes optical storage, magnetic tapeStill must be managedVaries between WORM (write-once, read-many-times) and RW (read-write)
33 CachingImportant principle, performed at many levels in a computer (in hardware, operating system, software)Information in use copied from slower to faster storage temporarilyFaster storage (cache) checked first to determine if information is thereIf it is, information used directly from the cache (fast)If not, data copied to cache and used thereCache smaller than storage being cachedCache management important design problemCache size and replacement policy
34 Performance of Various Levels of Storage Movement between levels of storage hierarchy can be explicit or implicit
35 Migration of Integer A from Disk to Register Multitasking environments must be careful to use most recent value, not matter where it is stored in the storage hierarchyMultiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cacheDistributed environment situation even more complexSeveral copies of a datum can existVarious solutions covered in Chapter 17
36 I/O SubsystemOne purpose of OS is to hide peculiarities of hardware devices from the userI/O subsystem responsible forMemory 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 interfaceDrivers for specific hardware devices
37 1.9 Protection and Security Protection: is any mechanism for controlling the access of processes or users to the resources defined by a computer system.This mechanism must provide means for specification of the controls to be imposed and means for enforcement.Protection can improve reliability by detecting latent errors at the interfaces between component subsystems.可防止不具權限者誤用系統A system can have adequate protection but still be prone to failure and allow inappropriate access.例如：一個人的ID&PW被盜用後，儘管file and memory protection機制仍在進行，她的資料還是可能被刪除或是被copy，這就是屬於security的範圍了。
38 1.9 Protection and Security Security – defense of the system against internal and external attacksHuge range, including denial-of-service, worms, viruses, identity theft, theft of serviceSystems generally first distinguish among users, to determine who can do whatUser identities (user IDs, security IDs) include name and associated number, one per userUser ID then associated with all files, processes of that user to determine access controlGroup identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, filePrivilege escalation allows user to change to effective ID with more rights
39 1.11 Special-Purpose Systems Real-Time Embedded SystemsMultimedia SystemsHandheld Systems
40 Real-Time Embedded Systems A real time systemis used when rigid time requirements have been placed on the operation of a processor or the flow of data; thus, it is often used as a control device in a dedicated application.has well-defined, fixed time constraintsprocessing must be done within the defined constraints, or the system will fail.Embedded systems tend to have very specific tasks.Embedded systems almost always run real-time operating systems.
41 1.12 Computing Environments Traditional computerBlurring over timeOffice environmentPCs connected to a network, terminals attached to mainframe or minicomputers providing batch and timesharingNow portals allowing networked and remote systems access to same resourcesHome networksUsed to be single system, then modemsNow firewalled, networked
42 Computing Environments (Cont.) Client-Server ComputingDumb terminals supplanted by smart PCsMany systems now servers, responding to requests generated by clientsCompute-server provides an interface to client to request services (i.e. database)File-server provides interface for clients to store and retrieve files
43 Peer-to-Peer Computing Another model of distributed systemP2P does not distinguish clients and serversInstead all nodes are considered peersMay each act as client, server or bothNode must join P2P networkRegisters its service with central lookup service on network, orBroadcast request for service and respond to requests for service via discovery protocol
44 Web-Based Computing Web has become ubiquitous PCs most prevalent devicesMore devices becoming networked to allow web accessNew category of devices to manage web traffic among similar servers: load balancersUse of operating systems like Windows 95, client-side, have evolved into Linux and Windows XP, which can be clients and servers
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