Transcription of Virtual Memory and Address Translation
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Virtual Memory and Address Translation
Virtual Memory andAddress Translation1 ReviewProgram addresses are Virtual addresses. Relative offset of program regions can not change during program execution. , heap can not move further from Virtual addresses == physical Address inconvenient. Program location is compiled into the single offset register allows the OS to place a process Virtual Address space anywhere in physical Memory . Virtual Address space must be smaller than physical. Program is swapped out of old location and swapped into creates external fragmentation and requires large 2ggqgregions of contiguous physical Memory . We look to fixed sized units, Memory pages, to solve the MemoryConceptKey problem: How can one support programs that require more Memory than is physically available? How can we support programs that do not use all of their Memory at once?2n-1 Hide physical size of Memory from users Memory is a large Virtual Address spaceof 2n bytes Only portions of VAS are in physical Memory at any one time (increase Memory utilization).
Address translation is ¾A. Frequent 9 ¾B. Infrequent Changing address mappings is ¾A. Frequent ¾B. Infrequent Paging Virtual address translation A page table maps virtual pages to physical frames (f,o) Program P CPU P’s Virtual Address Space Physical 20 910 1 Memory po 16 910 1 fo Virtual Add 10 Page Table (p,o) p Physical Addresses resses f
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