操作系统第一章 计算机系统概述.ppt

* Multiple Interrupts * Multiprogramming 多道 Processor has more than one program to execute The sequence the programs are executed depend on their relative priority and whether they are waiting for I/O After an interrupt handler completes, control may not return to the program that was executing at the time of the interrupt * Memory Hierarchy 存储层次 Faster access time, greater cost per bit Greater capacity, smaller cost per bit Greater capacity, slower access speed * Memory Hierarchy * Going Down the Hierarchy Decreasing cost per bit Increasing capacity Increasing access time Decreasing frequency of access of the memory by the processor Locality of reference * Secondary Memory 辅助存储器 Used to store program and data files Nonvolatile 非易失的 Auxiliary memory 辅助存储 * Disk Cache 磁盘高速缓存 A portion of main memory used as a buffer to temporarily to hold data for the disk Disk writes are clustered Some data written out may be referenced again. The data are retrieved rapidly from the software cache instead of slowly from disk * Cache Memory 高速缓存 Invisible to operating system Increase the speed of memory Processor speed is faster than memory speed Exploit the principle of locality * Cache Memory Contains a copy of a portion of main memory Processor first checks cache If not found in cache, the block of memory containing the needed information is moved to the cache and delivered to the processor * Cache/Main Memory System * Cache Read Operation * Cache Design Cache size Small caches have a significant impact on performance Block size The unit of data exchanged between cache and main memory Larger block size more hits until probability of using newly fetched data becomes less than the probability of reusing data that have to be moved out of cache * Cache Design Mapping function Determines which cache location the block will occupy Replacement algorithm Determines which block to replace Least-Recently-Used LRU algorithm * Cache Design Write policy When the memory write