操作系统原理121章节(988KB).ppt

Memory Protection Must provide memory protection at least for the interrupt vector and the interrupt service routines. In order to have memory protection, add two registers that determine the range of legal addresses a program may access: Base register （基址寄存器）– holds the smallest legal physical memory address. Limit register（界限寄存器） – contains the size of the range Memory outside the defined range is protected. Operating System Concepts Use of A Base and Limit Register Operating System Concepts Hardware Address Protection Operating System Concepts Hardware Protection When executing in monitor mode, the operating system has unrestricted access to both monitor and user’s memory. The load instructions for the base and limit registers are privileged instructions. Operating System Concepts CPU Protection Timer – interrupts computer after specified period to ensure operating system maintains control. Timer is decremented every clock tick. When timer reaches the value 0, an interrupt occurs. Timer commonly used to implement time sharing. Timer also used to compute the current time. Load-timer is a privileged instruction. Operating System Concepts Chapter 2: Computer-System Structures (6th Edition) 张竞慧 jhzhang@seu.edu.cn 九龙湖校区计算机楼366房间 电话 Chapter 2: Computer-System Structures (6th Ed.) Computer System Operation I/O Structure Storage Structure Storage Hierarchy Hardware Protection Network Structure Operating System Concepts Computer-System Architecture Operating System Concepts How does the OS get into system? How do we request for services? How does the OS know something has happened? How OS gets into system Operating System Concepts Operating System Concepts How Linux gets into system Computer-System Operation I/O devices and the CPU can execute concurrently. Each device controller is in charge of a particular device type. Each device controller has a local buffer. Operating System Concepts Computer-System Operation (Cont.) CPU moves data from/to main mem