Chapter_8

Chapter_8 - Chapter 8: Memory Management s Background s...

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8.1 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Chapter 8: Memory Management Chapter 8: Memory Management Background Swapping Contiguous Allocation Paging Segmentation Segmentation with Paging
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8.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Binding of Instructions and Data to Memory Binding of Instructions and Data to Memory 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.
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8.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Multistep Processing of a User Program Multistep Processing of a User Program
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8.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Logical vs. Physical Address Space 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.
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8.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Memory-Management Unit ( Memory-Management Unit ( MMU 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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8.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Dynamic relocation using a relocation register Dynamic relocation using a relocation register
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8.7 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Dynamic Loading Dynamic Loading A routine is not loaded until it is called. All routines are kept on disk in a relocatable load format. Better memory-space utilization; unused routine is never loaded. Useful when large amounts of code are needed to handle infrequently occurring cases such as error routines. No special support from the operating system is required. It is the responsibility of the users to design their programs to take advantage of this method. OS may help programmer by providing library routines to implement dynamic loading.
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8.8 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Dynamic Linking Dynamic Linking
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Chapter_8 - Chapter 8: Memory Management s Background s...

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