Tài liệu, ebook Tin Học Văn Phòng

Allocation/deallocation of memory can lead to fragmentation: internal or external First-fit, next-fit and best-fit strategies try to reduce fragmentation buddy systems and power-of-2 allocators eliminate external fragmentation Noncontiguous allocation reduces external fragmentation Requires use of the memory management unit (MMU) of CPU Kernel...

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Multiprocessor OS algorithms must be scalable Use of special kinds of locks: Spin locks and sleep locks Important scheduling concepts in multiprocessor OSs: Affinity scheduling Coscheduling Process shuffling

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Message passing paradigm realizes exchange of information among processes without using shared memory Useful in: microkernel-based OSs, client–server computing, higher-level communication protocols, and parallel or distributed programs Sender/receiver naming: symmetric, asymmetric, indirect (mailbox) Message passing is employed in higher-level p...

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Deadlock: set of processes wait indefinitely for events because each of the events can be caused only by other processes in the set Resource deadlock arises when: Resources are nonshareable and nonpreemptible Hold-and-wait Circular wait exists OS can discover a deadlock by analyzing the allocation state of a system Use RRAG, WFG or matrix mod...

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Different scheduling policies Time-sharing: Multilevel adaptive scheduling Fair share scheduling Real-time: Deadline scheduling Rate monotonic scheduling Performance analysis is used to study and tune performance of scheduling policies

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Process synchronization is a generic term for data access synchronization and control synchronization A race condition occurs when actions of concurrent processes may have unexpected consequences Avoided through mutual exclusion Avoidance of race conditions is a primary issue in process synchronization Critical section: section of code that acc...

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A thread is an alternative model of execution of a program Overhead of switching between threads is much less than the overhead of switching between processes Three models of threads: Kernel-level threads User-level threads Hybrid threads Thread models have different implications for switching overhead, concurrency, and parallelism

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Layered design used the principle of abstraction to control complexity of designing the OS The virtual machine operating system (VM OS) supported operation of several OSs on a computer simultaneously Create a virtual machine for each user In a kernel-based design, kernel is the core of the OS, which invokes the nonkernel routines to implement op...

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Evolution (continued) Real-time operating systems Priority-based scheduling and deadline-aware scheduling Distributed operating system Lets programs share resources across network Modern operating system Modern computing environment has elements of all the classic computing environments Uses different techniques for different applications

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Memory hierarchy provides the same effect as a fast and large memory, at a low cost Contains: A very fast and small cache memory A slower and larger RAM A disk Effective memory access time depends on cache hit ratio I/O system uses direct memory access (DMA) to permit CPU and I/O system to operate independently

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