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Chapter 2: Computer-System Structures

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Chapter 2: Computer-System Structures

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    1. Operating System Concepts Chapter 2: Computer-System Structures Computer System Operation I/O Structure Storage Structure Storage Hierarchy Hardware Protection General System Architecture

    2. Operating System Concepts Computer-System Architecture

    3. Operating System Concepts 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.

    4. Operating System Concepts 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.

    5. Operating System Concepts 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 vectored interrupt system Separate segments of code determine what action should be taken for each type of interrupt

    6. Operating System Concepts Interrupt Time Line For a Single Process Doing Output

    7. Operating System Concepts 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.

    8. Operating System Concepts Two I/O Methods

    9. Operating System Concepts Device-Status Table

    10. Operating System Concepts 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.

    11. Operating System Concepts Storage Structure Main 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 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.

    12. Operating System Concepts Moving-Head Disk Mechanism

    13. Operating System Concepts Storage Hierarchy Storage systems organized in hierarchy. Speed Cost Volatility Caching copying information into faster storage system; main memory can be viewed as a last cache for secondary storage.

    14. Operating System Concepts Storage-Device Hierarchy

    15. Operating System Concepts Caching Use of high-speed memory to hold recently-accessed data. Requires a cache management policy. Caching introduces another level in storage hierarchy. This requires data that is simultaneously stored in more than one level to be consistent.

    16. Operating System Concepts Migration of A From Disk to Register

    17. Operating System Concepts Hardware Protection Dual-Mode Operation I/O Protection Memory Protection CPU Protection

    18. Operating System Concepts Dual-Mode Operation Sharing system resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly. Provide hardware support to differentiate between at least two modes of operations. 1. User mode execution done on behalf of a user. 2. Monitor mode (also kernel mode or system mode) execution done on behalf of operating system.

    19. Operating System Concepts Dual-Mode Operation (Cont.) Mode bit added to computer hardware to indicate the current mode: monitor (0) or user (1). When an interrupt or fault occurs hardware switches to monitor mode.

    20. Operating System Concepts I/O Protection All I/O instructions are privileged instructions. Must ensure that a user program could never gain control of the computer in monitor mode (I.e., a user program that, as part of its execution, stores a new address in the interrupt vector).

    21. Operating System Concepts Use of A System Call to Perform I/O

    22. Operating System Concepts Memory Protection Must provide memory protection at least for the interrupt vector and the interrupt service routines. In order to have memory protection, add two registers that determine the range of legal addresses a program may access: Base register holds the smallest legal physical memory address. Limit register contains the size of the range Memory outside the defined range is protected.

    23. Operating System Concepts Use of A Base and Limit Register

    24. Operating System Concepts Hardware Address Protection

    25. Operating System Concepts Hardware Protection When executing in monitor mode, the operating system has unrestricted access to both monitor and users memory. The load instructions for the base and limit registers are privileged instructions.

    26. Operating System Concepts CPU Protection Timer interrupts computer after specified period to ensure operating system maintains control. Timer is decremented every clock tick. When timer reaches the value 0, an interrupt occurs. Timer commonly used to implement time sharing. Time also used to compute the current time. Load-timer is a privileged instruction.

    27. Operating System Concepts Network Structure Local Area Networks (LAN) Wide Area Networks (WAN)

    28. Operating System Concepts Local Area Network Structure

    29. Operating System Concepts Wide Area Network Structure

    30. Operating System Concepts Layers of Computer System

    31. Operating System Concepts Services Provided by the Operating System Program development Editors and debuggers Program execution Access to I/O devices Controlled access to files System access

    32. Operating System Concepts Services Provided by the Operating System Error detection and response internal and external hardware errors memory error device failure software errors arithmetic overflow access forbidden memory locations operating system cannot grant request of application

    33. Operating System Concepts Services Provided by the Operating System Accounting collect statistics monitor performance used to anticipate future enhancements used for billing users

    34. Operating System Concepts Operating System Functions same way as ordinary computer software It is program that is executed Operating system relinquishes control of the processor to execute other programs

    35. Operating System Concepts

    36. Operating System Concepts Kernel Portion of operating system that is in main memory Contains most-frequently used functions Also called the nucleus

    37. Operating System Concepts Uniprogramming Processor must wait for I/O instruction to complete before preceding

    38. Operating System Concepts Multiprogramming When one job needs to wait for I/O, the processor can switch to the other job

    39. Operating System Concepts Multiprogramming

    40. Operating System Concepts Major Achievements Processes Memory Management Information protection and security Scheduling and resource management System structure

    41. Operating System Concepts Processes A program in execution An instance of a program running on a computer The entity that can be assigned to and executed on a processor A unit of activity characterized by a single sequential thread of execution, a current state, and an associated set of system resources

    42. Operating System Concepts Process Consists of three components An executable program Associated data needed by the program Execution context of the program All information the operating system needs to manage the process

    43. Operating System Concepts Process

    44. Operating System Concepts Memory Management Process isolation Automatic allocation and management Support for modular programming Protection and access control Long-term storage

    45. Operating System Concepts Virtual Memory Allows programmers to address memory from a logical point of view While one process is written out to secondary store and the successor process read in there in no hiatus

    46. Operating System Concepts File System Implements long-term store Information stored in named objects called files

    47. Operating System Concepts Paging Allows process to be comprised of a number of fixed-size blocks, called pages Virtual address is a page number and an offset within the page Each page may be located any where in main memory Real address or physical address in main memory

    48. Operating System Concepts

    49. Operating System Concepts Virtual Memory Addressing

    50. Operating System Concepts Information Protection and Security Access control regulate user access to the system Information flow control regulate flow of data within the system and its delivery to users Certification proving that access and flow control perform according to specifications

    51. Operating System Concepts Scheduling and Resource Management Fairness give equal and fair access to all processes Differential responsiveness discriminate between different classes of jobs Efficiency maximize throughput, minimize response time, and accommodate as many uses as possible

    52. Operating System Concepts Major Elements of Operating System

    53. Operating System Concepts System Structure View the system as a series of levels Each level performs a related subset of functions Each level relies on the next lower level to perform more primitive functions This decomposes a problem into a number of more manageable subproblems

    54. Operating System Concepts Operating System Design Hierarchy

    55. Operating System Concepts Operating System Design Hierarchy

    56. Operating System Concepts Operating System Design Hierarchy

    57. Operating System Concepts Characteristics of Modern Operating Systems Microkernel architecture assigns only a few essential functions to the kernel address space interprocess communication (IPC) basic scheduling

    58. Operating System Concepts Characteristics of Modern Operating Systems Multithreading process is divided into threads that can run simultaneously Thread dispatchable unit of work executes sequentially and is interruptable Process is a collection of one or more threads

    59. Operating System Concepts Characteristics of Modern Operating Systems Symmetric multiprocessing there are multiple processors these processors share same main memory and I/O facilities All processors can perform the same functions

    60. Operating System Concepts Characteristics of Modern Operating Systems Distributed operating systems provides the illusion of a single main memory and single secondary memory space used for distributed file system

    61. Operating System Concepts Characteristics of Modern Operating Systems Object-oriented design used for adding modular extensions to a small kernel enables programmers to customize an operating system without disrupting system integrity

    62. Operating System Concepts Client/Server Model Simplifies the Executive possible to construct a variety of APIs Improves reliability each service runs as a separate process with its own partition of memory clients cannot not directly access hardware Provides a uniform means fro applications to communicate via LPC Provides base for distributed computing

    63. Operating System Concepts Threads and SMP Different routines can execute simultaneously on different processors Multiple threads of execution within a single process may execute on different processors simultaneously Server processes may use multiple threads Share data and resources between process

    64. Operating System Concepts

    65. Operating System Concepts UNIX Hardware is surrounded by the operating-system Operating system is called the kernel Comes with a number of user services and interfaces shell C compiler

    66. Operating System Concepts UNIX

    67. Operating System Concepts Modern UNIX Systems System V Release 4 (SVR4) Solaris 2.x 4.4BSD Linux

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