CS345 07 - Memory Management

CS345 07 - Memory Management - Chapter 7 Memory Management...

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Chapter 7 Memory Management
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BYU CS 345 Computer Systems 2 Memory Management Requirements Relocation Users generally don’t know where they will be placed in main memory May swap in at a different place (pointers???) Generally handled by hardware Protection Prevent processes from interfering with the O.S. or other processes Often integrated with relocation Sharing Allow processes to share data/programs Logical Organization Support modules, shared subroutines Physical Organization Main memory verses secondary memory Overlaying Requirements
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BYU CS 345 Computer Systems 3 Address Binding A process must be tied to a physical address at some point (bound) Binding can take place at 3 times Compile time Always loaded to same memory address Load time relocatable code stays in same spot once loaded Execution time may be moved during execution special hardware needed source object Compiler/Assembler load module Linker Loader Executable
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BYU CS 345 Computer Systems 4 Memory Management Techniques Fixed Partitioning Divide memory into partitions at boot time, partition sizes may be equal or unequal but don’t change Simple but has internal fragmentation Dynamic Partitioning Create partitions as programs loaded Avoids internal fragmentation, but must deal with external fragmentation Simple Paging Divide memory into equal-size pages, load program into available pages No external fragmentation, small amount of internal fragmentation
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BYU CS 345 Computer Systems 5 Simple Segmentation Divide program into segments No internal fragmentation, some external fragmentation Virtual-Memory Paging Paging, but not all pages need to be in memory at one time Allows large virtual memory space More multiprogramming, overhead Virtual Memory Segmentation Like simple segmentation, but not all segments need to be in memory at one time Easy to share modules More multiprogramming, overhead Memory Management Techniques
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BYU CS 345 Computer Systems 6 Fixed Partitioning Main memory divided into static partitions Simple to implement Inefficient use of memory Small programs use entire partition Maximum active processes fixed Internal Fragmentation 8 M 8 M 8 M 8 M 8 M Operating System
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CS345 07 - Memory Management - Chapter 7 Memory Management...

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