6 - Storage Structure Main memory only large storage media...

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Storage Structure Main memory – only large storage media that the CPU can access directly Secondary storage – extension of main memory that provides large nonvolatile storage capacity Magnetic disks – rigid metal or glass platters covered with magnetic recording material Disk surface is logically divided into tracks , which are subdivided into sectors The disk controller determines the logical interaction between the device and the computer
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Storage Hierarchy Storage systems organized in hierarchy Speed Cost Volatility Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage
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Storage-Device Hierarchy
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Caching Use of high-speed memory to hold recently- accessed data Requires a cache management policy Caching introduces another level in storage hierarchy. This requires data that is simultaneously stored in more than one level to be consistent
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Migration of Integer “A” From Disk to Register
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Hardware Protection Dual-Mode Operation I/O Protection Memory Protection CPU Protection
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Dual-Mode Operation Sharing system resources requires operating system to ensure that an incorrect program or poorly behaving human cannot cause other programs to execute incorrectly OS must provide hardware support to differentiate between at least two modes of operations 1. User mode – execution done on behalf of a user 2. Monitor mode (also kernel mode or system mode ) – execution done on behalf of operating system
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Dual-Mode Operation (Cont.) Mode bit added to computer hardware to indicate the current mode: monitor (0) or user (1) When an interrupt or fault occurs hardware switches to monitor mode Privileged instructions can be issued only in monitor mode monitor user Interrupt/fault set user mode
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I/O Protection All I/O instructions are privileged instructions Must ensure that a user program could never gain control of the computer in monitor mode (I.e., a user program that, as part of its execution, stores a new address in the interrupt vector)
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Use of A System Call to Perform I/O
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Memory Protection Must provide memory protection at least for the interrupt vector and the interrupt service routines In order to have memory protection, at a minimum 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
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Use of A Base and Limit Register
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Hardware Address Protection
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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
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CPU Protection Timer – interrupts computer after specified period to ensure operating system maintains control Timer is decremented every clock tick
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This note was uploaded on 03/14/2010 for the course CSE SSZG516 taught by Professor Muralip during the Summer '10 term at Birla Institute of Technology & Science.

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6 - Storage Structure Main memory only large storage media...

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