Use of A System Call to Perform I/O Silberschatz, Galvin and Gagne 2002 2.22 Operating System Concepts 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 – holds the smallest legal physical memory address. ✦ Limit register – contains the size of the range ■ Memory outside the defined range is protected.
Silberschatz, Galvin and Gagne 2002 2.23 Operating System Concepts Use of A Base and Limit Register Silberschatz, Galvin and Gagne 2002 2.24 Operating System Concepts Hardware Address Protection
Silberschatz, Galvin and Gagne 2002 2.25 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. Silberschatz, Galvin and Gagne 2002 2.26 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. ■ Time also used to compute the current time. ■ Load-timer is a privileged instruction.
Silberschatz, Galvin and Gagne 2002 2.27 Operating System Concepts Network Structure ■ Local Area Networks (LAN) ■ Wide Area Networks (WAN) Silberschatz, Galvin and Gagne 2002 2.28 Operating System Concepts Local Area Network Structure
Silberschatz, Galvin and Gagne 2002 2.29 Operating System Concepts Wide Area Network Structure
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- Spring '18