L8-VirtualMemory

L8-VirtualMemory - Virtual Memory Organization Management...

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Virtual Memory Organization & Management CSIS0230A Lecture Eight Concepts Virtual memory Address translation Paging Segmentation Fetching strategies Replacement strategies Thrashing
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Recommended Readings Section Chapter 10 and 11 of Operating Systems, 3rd edition by Deitel et. al CSIS0230A Principles of Operating Systems 2
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References Section Chapter 10 and 11 of Operating Systems, 3rd edition by Deitel et. al Chapter 6 of Operating Systems - A Concept- Based Approach, 2nd edition by D.M. Dhamdhere Chapter 8 of Operating Systems: Internal and Design Principles, 6th edition by William Stallings Chapter 9 of Operating System Principles, 7th edition by Silberschatz et. al CSIS0230A Principles of Operating Systems 3
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Memory Allocation [Reiterate] Ways of organizing programs in memory Contiguous allocation We have discussed this in Lecture Seven Noncontiguous allocation Program address space is divided into chunks Each chunk can be placed in different part of memory Easier to find “free slots” in memory, in which a chunk will fit Increased number of processes that can exist simultaneously in memory offsets the overhead incurred by this technique Example - virtual memory management 4 CSIS0230A Principles of Operating Systems
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Virtual Memory Solves problem of limited memory space Creates the illusion that more physical memory exists than is available in system Two types of addresses in virtual memory systems Virtual addresses Referenced by processes Physical addresses Describes locations in main memory CSIS0230A Principles of Operating Systems 5
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Virtual Memory Virtual address space, V Range of virtual addresses that a process may reference 32-bit 2 32 = 4 GiBytes Real address space, R Range of physical addresses available on a computer |V| is often much greater than |R| OS must store parts of Virtual Memory for each process outside of main memory Between main memory and secondary storage CSIS0230A Principles of Operating Systems 6
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Virtual Memory Dynamic address translation (DAT) mechanism Converts virtual address to physical address during program execution Must be very fast as being invoked for every instruction executed Memory management unit (MMU) Special-purpose hardware for quickly translating virtual addresses to physical address CSIS0230A Principles of Operating Systems 7
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Address Mapping Address translation maps Indicate which regions of a process’s virtual address space V, are currently in main memory and where they are located If granularity is too fine, large amount of mapping info Block The larger the block size, the smaller amount of the mapping information If too large block, may suffer with internal fragmentation and take longer time to load a block Pages Blocks that are of fixed size Technique is called paging Segments Blocks maybe of different size Technique is called segmentation CSIS0230A Principles of Operating Systems 8
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