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Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
Basic os-concepts
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Basic os-concepts

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Basic OS Concepts

Basic OS Concepts

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  • 1. Introduction to Basic OSConcepts
  • 2. Introduction What is an Operating System? Mainframe Systems Desktop Systems Multiprocessor Systems Distributed Systems Clustered System Real -Time Systems Handheld Systems
  • 3. What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware. 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.
  • 4. What is OS? Computer systems typically contain: Hardware and Software Hardware - electronic, mechanical, optical devices Software – programs Without support software, the computer is of little use..
  • 5. What is OS? An interface between Hardware and User Programs An abstraction of the hardware for all the (user) processes  Hide the complexity of the underlying hardware and give the user a better view of the computer => A MUST!
  • 6. Computer System Components1. Hardware – provides basic computing resources (CPU, memory, I/O devices).2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs).4. Users (people, machines, other computers).
  • 7. Abstract View of SystemComponents
  • 8. The OS applications utilities software systems software Operating system hardware device device ... devicecomponents CPU memory
  • 9. Operating System Definitions Resource allocator – manages and allocates resources. Control program – controls the execution of user programs and operations of I/O devices . Kernel – the one program running at all times (all else being application programs).
  • 10. The Goals of an OS Let users run programs:  Correctness  Memory boundaries, priorities, steady state  Convenience  User should not handle the tiny details (encapsulate/abstract), provide synchronization primitives, system calls, file system, tools
  • 11. The Goals of an OS Let users run programs:  Efficiency  Resource Utilization, resource Sharing, Multitasking  Fairness (in resource allocation)  Among: users, tasks, resources  The tradeoff between efficiency and fairness
  • 12. An OS is a Resource Allocator “Mama says: It’s good to share!” Multiple users (?) get all computing resources “simultaneously”:  Cpu time  Memory (ram, swap, working set, virtual,..)  File system (storage space)  I/O devices (display, printers, mouse,..)  Clock The OS should give every user the illusion that she is getting all resources to herself (not sharing!)
  • 13. What an OS does for a living..loop forever { run the process for a while. stop process and save its state. load state of another process. }
  • 14. Virtual Continuity A process can get “switched in” or “switched out”. OS should give the illusion for the process as if it exists in the CPU continuously => Context Switching
  • 15. Context switching When an event occurs, the operating system saves the state of the active process and restores the state of the new process. This mechanism is called a Context Switch. What must get saved? Everything that the next process could or will damage. For example:  Program counter (PC)  Program status word (PSW)  CPU registers (general purpose, floating-point)  File access pointer(s)  Memory (perhaps?)
  • 16. Scheduling and Context switch A process can give up the cpu:  A. by performing I/O (e.g. getchar())  B. by entering a waiting state (e.g. semaphore)  C. by entering a suspended state (e.g. sleep()) Give up the CPU == switch out the current process + switch in another process
  • 17. Preemptive Scheduling There are OS’s where a process is forced to give up the cpu (e.g. when stayed for too long). Such systems are implementing a “preemptive scheduling” policy.  Examples include Windows NT, Unix, - BUT NOT - Windows prior to Win95 ! or Macintosh!  Xinu? Should a real-time system implement preemptive scheduling?
  • 18. Using Priorities Most OS’s provide the priority mechanism Priorities are associated with processes Priority are used to help the OS to reach fairness Can you think of processes (e.g. in Windows) for which you will give especially high/low priority ??
  • 19. Process A process is a program in execution. The components of a process are:  the program to be executed,  the data on which the program will execute,  the resources required by the program—such as memory and file(s)—and  the status of the execution.
  • 20. ‫‪Process Interleaving‬‬ ‫תהליכים עוקבים‬ ‫תהליכים מקבילים‬ ‫‪A‬‬ ‫‪C‬‬ ‫‪D‬‬ ‫‪B‬‬ ‫ציר‬ ‫הזמן‬
  • 21. Mainframe Systems Reduce setup time by batching similar jobs Automatic job sequencing – automatically transfers control from one job to another. First rudimentary operating system. Resident monitor  initial control in monitor  control transfers to job  when job completes control transfers pack to monitor
  • 22. Memory Layout for a Simple BatchSystem
  • 23. Multiprogrammed Batch SystemsSeveral jobs are kept in main memory at the same time, and theCPU is multiplexed among them.
  • 24. OS Features Needed forMultiprogramming 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.
  • 25. Time-Sharing Systems–Interactive Computing The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory). A job swapped in and out of memory to the disk. 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 system must be available for users to access data and code.
  • 26. Desktop Systems Personal computers – computer system dedicated to a single user. I/O devices – keyboards, mice, display screens, small printers. User convenience and responsiveness. Can adopt technology developed for larger operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features. May run several different types of operating systems (Windows, MacOS, UNIX, Linux)
  • 27. Parallel Systems Multiprocessor systems with more than on CPU in close communication. Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. Advantages of parallel system:  Increased throughput  Economical  Increased reliability  graceful degradation  fail-soft systems
  • 28. Parallel Systems (Cont.) Symmetric multiprocessing (SMP)  Each processor runs and 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
  • 29. Symmetric MultiprocessingArchitecture
  • 30. 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. Advantages of distributed systems.  Resources Sharing  Computation speed up – load sharing  Reliability  Communications
  • 31. Distributed Systems (cont) Requires networking infrastructure. Local area networks (LAN) or Wide area networks (WAN) May be either client-server or peer- to-peer systems.
  • 32. General Structure of Client-Server
  • 33. Clustered Systems Clustering allows two or more systems to share storage. Provides high reliability. Asymmetric clustering: one server runs the application while other servers standby. Symmetric clustering: all N hosts are running the application.
  • 34. 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. Real-Time systems may be either hard or soft real-time.
  • 35. Real-Time Systems (Cont.) Hard real-time:  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  Limited utility in industrial control of robotics  Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.
  • 36. Handheld Systems Personal Digital Assistants (PDAs) Cellular telephones Issues:  Limited memory  Slow processors  Small display screens.
  • 37. Migration of Operating-SystemConcepts and Features
  • 38. Computing Environments Traditional computing Web-Based Computing Embedded Computing
  • 39. The PC-XINU OS Let’s fillin’ the bits..

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