os9 - Modified from Lecture Slides for Operating System...

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Operating Systems : Memory Management (Chapter 9) Sung-Yong Park, Ph.D. Department of Computer Science Sogang University Modified from Lecture Slides for Operating System Concepts (6 th Edition) by Silberschatz et. al. Page 2 Background ± Program must be brought into memory and placed within a process for it to be run. ± Input queue – collection of processes on the disk that are waiting to be brought into memory to run the program. ± User programs go through several steps before being run.
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Page 3 Address Binding ± Compile time : If memory location known a priori, absolute code can be generated; must recompile code if starting location changes. ± Load time : Must generate relocatable code if memory location is not known at compile time. ± Execution time : Binding delayed until run time if the process can be moved during its execution from one memory segment to another. Need hardware support for address maps (e.g., base and limit registers ). Address binding of instructions and data to memory addresses can happen at three different stages. Page 4 Multi-step Processing of User Program
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Page 5 Logical vs. Physical Address Space ± The concept of a logical address space that is bound to a separate physical address space is central to proper memory management. ± Logical address – generated by the CPU; also referred to as virtual address . ± Physical address – address seen by the memory unit. ± Logical and physical addresses are the same in compile-time and load-time address-binding schemes; logical (virtual) and physical addresses differ in execution-time address-binding scheme. Page 6 Memory Management Unit (MMU) ± Hardware device that maps virtual to physical address. ± In MMU scheme, the value in the relocation register is added to every address generated by a user process at the time it is sent to memory. ± The user program deals with logical addresses; it never sees the real physical addresses.
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Page 7 Dynamic Loading vs. Dynamic Linking ± Dynamic Loading ± Routine is not loaded until it is called ± Better memory-space utilization; unused routine is never loaded. ± Useful when large amounts of code are needed to handle infrequently occurring cases. ± No special support from the operating system is required implemented through program design. ± Dynamic Linking
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This note was uploaded on 01/20/2010 for the course CS CSE407001 taught by Professor Psy during the Fall '03 term at Sogang University.

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os9 - Modified from Lecture Slides for Operating System...

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