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Bare Machine (early 1950s)

Bare Machine (early 1950s). Structure Large machines run from console Single user system Programmer/User as operator Paper tape or punched cards Early Software Assemblers, compilers, linkers, loaders Libraries of common subroutines Device drivers Inefficient use of expensive resources

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Bare Machine (early 1950s)

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  1. Bare Machine (early 1950s) • Structure • Large machines run from console • Single user system • Programmer/User as operator • Paper tape or punched cards • Early Software • Assemblers, compilers, linkers, loaders • Libraries of common subroutines • Device drivers • Inefficient use of expensive resources • Low CPU utilization • Significant amount of setup time • Solutions • Add a card reader • Hire an operator Operating System Concepts

  2. Simple Batch Systems • Reduce setup time by batching similar jobs • Automatic job sequencing - automatically transfers control from one job to another - first rudimentary OS • Resident monitor • Initial control in monitor • Control transfers to job • Job transfers control back to monitor (or chaos ensues) • Use control cards to • Separate jobs • Specify job types, e.g., FORTRAN • Separate code from data Operating System Concepts

  3. Memory Layout for a Simple Batch System Operating System Concepts

  4. Offline Operation • Do card reading and printing offline • Jobs copied from cards to tape • Tape loads to CPU, and results output to tape • Tape content printed • Advantages • CPU constrained only by tape speed • No changes to existing code • Multiple card readers and printers per CPU Operating System Concepts

  5. Offline Operation Layout Operating System Concepts

  6. Spooling • Overlap I/O of one job with computation of another job. While executing one job, the OS: • Reads next job from card reader into a storage area on the disk (job queue). • Outputs printout of previous job from disk to printer. • Job pool – data structure that allows the OS to select which job to run next in order to increase CPU utilization • Critical change of hardware • Allows CPU to swap between IO control and job • Implemented with interrupts Operating System Concepts

  7. Spooling Operating System Concepts

  8. Two I/O Methods Synchronous Asynchronous Operating System Concepts

  9. Synchronous IO • After I/O starts, control returns to user program only upon I/O completion. • Wait instruction idles the CPU until the next interrupt • At most one I/O request is outstanding at a time, no simultaneous I/O processing. • More common in real time systems Asynchronous IO • 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 • IO device interrupts on completion • I/O devices and the CPU can execute concurrently. Operating System Concepts

  10. Asynchronous IO Request • User process requests IO service • Device-status table contains entry for each I/O device indicating its type, address, and state • If device is idle the IO starts • If the device is busy, the request is queued (double buffering) Operating System Concepts

  11. Asynchronous IO • Each device controller has a local buffer. • CPU moves data from/to memory to/from local buffers • Device controller informs CPU that it has finished its operation by causing an interrupt. • On interrupt the OS indexes into I/O device table to determine device status and do service • Feed more data from this request • Start next request on queue • Note device idle Operating System Concepts

  12. Multiprogrammed Batch Systems • Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. Operating System Concepts

  13. OS Features Needed for Multiprogramming • I/O routine supplied by the system. • Memory management – the system must allocate the memory to several jobs. • CPU scheduling – the system must choose among several jobs ready to run. • Allocation of devices. Operating System Concepts

  14. Time-Sharing Interactive Computing • Multi-programming plus … • Multi-user • On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard. • On-line file system must be available for users to access data and code • Jobs may be swapped in and out of memory to the disk. Operating System Concepts

  15. Dual-Mode Operation • 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. • 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 • When executing in monitor mode, the operating system has unrestricted access to both monitor and user’s memory. • Privileged instructions can be issued only in monitor mode. Interrupt/fault monitor user set user mode Operating System Concepts

  16. 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. • Timer also used to compute the current time. • Load-timer is a privileged instruction. • Setting the interrupt vector is privileged Operating System Concepts

  17. Memory Protection • 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. • The load instructions for the base and limit registers are privileged instructions. Operating System Concepts

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

  19. I/O Protection • All I/O instructions are privileged instructions. Operating System Concepts

  20. Personal Computers • Computer system dedicated to a single user. • I/O devices – keyboards, mice, display screens, small printers. • Goals: User convenience and responsiveness. • Can adopt technology developed for larger operating systems • Individuals have sole use of computer - only multi-programming. • May run several different types of operating systems (Windows, MacOS, UNIX, Linux) Operating System Concepts

  21. Multiprocessor Systems • Multiprocessor systems with more than one CPU in close communication. • Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. Operating System Concepts

  22. Multiprocessor Systems • Symmetric multiprocessing (SMP) • Each CPU runs an identical copy of the operating system. • Many processes can run at once without performance deterioration. • Most modern operating systems support SMP • Asymmetric multiprocessing • Each processor is assigned a specific task; master processor schedules and allocated work to slave processors. • More common in extremely large systems • Advantages of multiprocessor systems: • Increased throughput • Economical • Increased reliability • Graceful degradation • Fail-soft systems Operating System Concepts

  23. Distributed Systems • Distribute the computation among several physical processors. • Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines. • May be either client-server or peer-to-peer systems. Operating System Concepts

  24. Distributed Systems (cont) • Requires networking infrastructure. • Local area networks (LAN) or Wide area networks (WAN) • Advantages of distributed systems. • Resources Sharing • Computation speed up – load sharing • Reliability • Communications Operating System Concepts

  25. Real-Time Systems • Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. • Well-defined fixed-time constraints. • Hard real-time: guaranteed task completion • Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM) • Conflicts with time-sharing systems, not supported by general-purpose operating systems. • Soft real-time: absolute task priority • Limited utility in industrial control of robotics • Useful in applications (multimedia, virtual reality) requiring advanced operating-system features. Operating System Concepts

  26. Handheld Systems • Personal Digital Assistants (PDAs) • Cellular telephones • Issues: • Limited memory • Slow processors • Small display screens. Operating System Concepts

  27. Migration of Operating-System Concepts and Features Operating System Concepts

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