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Operating System

Operating System. Control program for the execution of application programs An interface between applications and hardware An intermediary between a user of a computer and the computer hardware. Operating System Objectives. Convenience Makes the computer more convenient to use

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Operating System

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  1. Operating System • Control program for the execution of application programs • An interface between applications and hardware • An intermediary between a user of a computer and the computer hardware CIS 340

  2. Operating System Objectives • Convenience • Makes the computer more convenient to use • Efficiency • Allows computer system resources to be used in an efficient manner • Ability to evolve • Permit effective development, testing, and introduction of new system functions without interfering with service

  3. Layers of Computer System CIS 340

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

  5. 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

  6. Services Provided by the Operating System • Accounting • Collect usage statistics • Monitor performance • Used to anticipate future enhancements • Used for billing purposes

  7. Operating System: Other Services • Allows multiple, concurrent computations • Allows through enabling resources allocation • Controls interactions between concurrent computations • Enforces rules to securely execute the computations without losing integrity • Supports interactions of computations among different computer systems • Handles networking interactions CIS 340

  8. Operating System Definitions Resource allocator • Manages and allocates resources Control program • Controls the execution of user programs • Controls operations of I/O devices Kernel • Portion of operating system running at all times in main memory • All and anything else being application programs • Contains most frequently used functions • Also called the nucleus CIS 340

  9. Migration of OS Concepts and Features through Platforms Batch TIME SHARE CIS 340

  10. Computer-System Architecture • Control Unit • Arithmetic / Logic Unit • Memory CIS 340

  11. Hardware Features HW realization supporting OS services • Memory protection • Do not allow the memory area containing the monitor to be altered • User program executes in user mode • Certain instructions may not be executed • Monitor executes in system mode • Kernel mode • Privileged instructions are executed • Protected areas of memory may be accessed CIS 340

  12. Hardware Features HW realization supporting OS services • Timer • Prevents a job from monopolizing the system • Privileged instructions • Certain machine level instructions to be executed only by the monitor • Interrupts • Early computer models did not have this capability CIS 340

  13. Computer-System Operation: Premises • I/O devices and the CPUcan execute concurrently • Each device controller handles 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 • Interrupt generated by device controller informs CPU about end of controller’s task CIS 340

  14. Def: Interrupts: Expectations • Transfers control to the interrupt service routine • Interrupt vector contains the addresses of all the service routines • Interrupt architecture saves the address of the interrupted instruction • A trap is a software-generated interrupt caused either by an error or a user request. • An operating system is interrupt driven CIS 340

  15. Interrupt service routine (ISR) • An interrupt handler, • also known as an interrupt service routine (ISR), • is a callback subroutine in an operating system or device driver • whose execution is triggered by the reception of an interrupt. • have a multitude of functions, which vary based on the reason the interrupt was generated and the speed at which the interrupt handler completes its task. • An interrupt handler is a low-level counterpart of event handlers. • These handlers are initiated by either hardware interrupts or interrupt instructions in software, • used for servicing hardware devices and transitions between protected modes of operation such as system calls. CIS 340

  16. Interrupt vector • In computing, an interrupt vector is • the memory address of an interrupt handler, • or an index into an array called an interrupt vector table or dispatch table containing the memory addresses of interrupt handlers. • When an interrupt is generated, • the processor saves its execution state via a context switch, and • begins execution of the interrupt handler at the interrupt vector. CIS 340

  17. I/O Devices Sloooooooooooow EX: System Utilization: CIS 340

  18. EX: Uniprogramming Processor must wait for I/O instruction to complete before preceding Processor must wait for I/O instruction to complete before preceding CIS 340

  19. EX: Multiprogrammingwith Three Programs Processor experiences less lapses CIS 340

  20. CONSIDER:Utilization Histograms CIS 340

  21. EX:Sample Program Execution Attributes CIS 340

  22. EX: Typical I/O Rates for Devices CIS 340

  23. 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

  24. Process

  25. Memory Management • Process isolation • Automatic allocation and management • Support of modular programming • Protection and access control • Long-term storage

  26. Virtual Memory • Allows programmers to address memory from a logical point of view • No hiatus between the execution of successive processes while one process was written out to secondary store and the successor proceess was read in

  27. Virtual Memory and File System • Implements long-term store • Information stored in named objects called files

  28. 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

  29. Virtual Memory

  30. Virtual Memory Addressing

  31. CIS 340

  32. OS Key Elements CIS 340

  33. Problems Arising with System Software • Improper synchronization • Ensure a process waiting for an I/O device receives the signal • Failed mutual exclusion • Memory overwrites • Nondeterminate program operation • Program A should only depend on input to it • Activities of other programs should not influence Program A’s outcome • Deadlocks CIS 340

  34. System Structure • 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 LEVELS (1-4) Process Hardware Levels (5-7) Concepts with Multiprogramming (8-13) Deal with External Objects CIS 340

  35. Process Hardware Levels • Level 1 • Electronic circuits • Objects are registers, memory cells, and logic gates • Operations are clearing a register or reading a memory location • Level 2 • Processor’s instruction set • Operations such as add, subtract, load, and store • Level 3 • Adds the concept of a procedure or subroutine, plus call/return operations • Level 4 • Interrupts CIS 340

  36. Concepts with Multiprogramming • Level 5 • Process as a program in execution • Suspend and resume processes • Level 6 • Secondary storage devices • Transfer of blocks of data • Level 7 • Creates logical address space for processes • Organizes virtual address space into blocks CIS 340

  37. Deal with External Objects (p 1 / 2) • Level 8 • Communication of information and messages between processes • Level 9 • Supports long-term storage of named files • Level 10 • Provides access to external devices using standardized interfaces CIS 340

  38. Deal with External Objects (p 2 / 2) • Level 11 • Maintains the association between the external and internal identifiers • Level 12 • Provides full-featured facility for the support of processes • Level 13 • Provides an interface to the operating system for the user CIS 340

  39. Modern Operating Systems: Concepts • Microkernel architecture • Multithreading • Symmetric multiprocessing (SMP) CIS 340

  40. Modern Operating Systems • Distributed operating systems • Provides the illusion of a single main memory space and single secondary memory space

  41. 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

  42. Windows Architecture • Modular structure for flexibility • Executes on a variety of hardware platforms • Supports application written for other operating system

  43. Operating System Organization • Modified microkernel architecture • Not a pure microkernel • Many system functions outside of the microkernel run in kernel mode • Any module can be removed, upgraded, or replaced without rewriting the entire system

  44. Kernel-Mode Components • Executive • Contains base operating system services • Memory management • Process and thread management • Security • I/O • Interprocess communication • Kernel • Consists of the most used components

  45. Kernel-Mode Components • Hardware abstraction layer (HAL) • Isolates the operating system from platform-specific hardware differences • Device drivers • Translate user I/O function calls into specific hardware device I/O requests • Windowing and graphics systems • Implements the graphical user interface (GUI)

  46. Windows Executive • I/O manager • Cache manager • Object manager • Plug and play manager • Power manager • Security reference monitor • Virtual memory manager • Process/thread manager • Configuration manager • Local procedure call (LPC) facility

  47. User-Mode Processes • Special system support processes • Ex: logon process and the session manager • Service processes • Environment subsystems • User applications

  48. Client/Server Model • Simplifies the Executive • Possible to construct a variety of APIs • Improves reliability • Each service runs on a separate process with its own partition of memory • Clients cannot not directly access hardware • Provides a uniform means for applications to communicate via LPC • Provides base for distributed computing

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