operatingsystemoverview(文件)
【正文】 ions may not be executed ? Monitor executes in system mode ? Kernel mode ? Privileged instructions are executed ? Protected areas of memory may be accessed 19 Batch operating system ? Machine time alternates between execution of user programs and execution of the monitor ? Two sacrifices: ? Some main memory is now given over to the monitor ? Some machine time is consumed by the monitor 20 I/O Devices Slow The puter spends over 96% of its time waiting for I/O devices to finish transferring data 21 Uniprogramming(單道程序 ) ?Processor must wait for I/O instruction to plete before preceding 22 Multiprogramming(多道程序 ) ?When one job needs to wait for I/O, the processor can switch to the other job 23 Multiprogramming 24 Example 25 Utilization Histograms(利用率 ) 26 Multiprogramming ? The most notable additional feature that is useful for Multiprogramming is the hardware that supports I/O interrupts and DMA. ? To have several jobs ready to run, they must be kept in main memory, requiring some form of memory management. ? It also requires some algorithm for scheduling. 27 TimeSharing Systems(分時(shí)系統(tǒng) ) ?Using multiprogramming to handle multiple interactive(交互式 ) jobs ?Processor’s time is shared among multiple users ?Multiple users simultaneously access the system through terminals ?The OS interleave the execution of each user program in a short time 28 Compatible TimeSharing System (CTSS) ? First timesharing system developed at MIT 29 Some new problems ? If multiple jobs are in memory, then they must by protected from interfering with each other ? With multiple interactive users, the file system must be protected so that only authorized users have access to a particular file ? Handle the contention for resources 30 Major Achievements ? Processes（ 進(jìn)程） ? Memory Management（ 存儲(chǔ)器管理） ? Information protection and security（ 信息保護(hù)和安全
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