Tài liệu, ebook Công Nghệ Thông Tin

Using local clocks in processes Logical clocks Vector clocks Include process ids in timestamps for total ordering It is not possible to record the global state of a system Chandy-Lamport algorithm obtains consistent recording of process states using special messages called markers

28 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1095 | Lượt tải: 0

Security and protection measures are used to counter interference threats Use authentication and authorization techniques Threats launched using Trojan horses, viruses, worms, and exploitation of buffer overflows Encryption is an algorithmic transformation of data Block ciphers and stream ciphers Widely used encryption standards: DES and AES ...

41 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1175 | Lượt tải: 0

An access method improves the performance of a file processing activity within a process using buffering and blocking of records Caching reduces the number of I/O operations performed to access data stored in files Physical IOCS implements a disk cache An access method implements a file cache The virtual memory handler uses a page cache OSs us...

53 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1154 | Lượt tải: 0

Files are structured or unstructured (byte stream) File system provides: File organizations (sequential, direct, indexed) Directories for grouping of related files logically Sharing and protection of files Disk space allocation, typically indexed File map table (FMT) stores allocation information File control block (FCB) stores information a...

65 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1195 | Lượt tải: 0

Which page should VM manager remove from memory to make space for a new page? Page replacement algorithms exploit locality of reference LRU has stack property, but is expensive NRU algorithms are used in practice E.g., clock algorithms How much memory should manager allocate? Use working set model to avoid thrashing Copy-on-write can be used...

57 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1238 | Lượt tải: 0

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...

50 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1051 | Lượt tải: 0

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

30 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1004 | Lượt tải: 0

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...

26 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 993 | Lượt tải: 0

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...

41 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1194 | Lượt tải: 0

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

54 trang | Chia sẻ: nguyenlam99 | Ngày: 10/01/2019 | Lượt xem: 1125 | Lượt tải: 0