memory management - part 2 (8)

memory management - part 2 (8) - COP 4600 Summer 2011...

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COP 4600: Intro To OS (Memory Management – Part 2) Page 1 © Dr. Mark Llewellyn COP 4600 – Summer 2011 Introduction To Operating Systems Memory Management – Part 2 Department of Electrical Engineering and Computer Science Computer Science Division University of Central Florida Instructor : Dr. Mark Llewellyn markl@cs.ucf.edu HEC 236, 407-823-2790 http://www.cs.ucf.edu/courses/cop4600/sum2011
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COP 4600: Intro To OS (Memory Management – Part 2) Page 2 © Dr. Mark Llewellyn Memory Management Memory Management Methods Contiguous Allocation Non-Contiguous Allocation Single Partition Multiple Partition Fixed Allocation Dynamic Allocation Segmentation Paging "Basic" Paging Demand Paging (Virtual Memory)
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COP 4600: Intro To OS (Memory Management – Part 2) Page 3 © Dr. Mark Llewellyn Paging Both unequal fixed-size and variable-size partitions are inefficient in the use of memory. Unequal fixed-size partitions result in internal fragmentation. Variable size partitions result in external fragmentation. Paging is a technique which attempts to resolve both types of fragmentation. In paging, the main memory is partitioned into fixed-size chunks that are relatively small, and each process is also divided into small fixed- size chunks of the same size. The chunks of a process are referred to as pages , while the chunks of main memory are referred to as frames (or page frames ). Paging results in a small amount of internal fragmentation in only the last frame assigned to a process and no external fragmentation.
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COP 4600: Intro To OS (Memory Management – Part 2) Page 4 © Dr. Mark Llewellyn Assignment of Process Pages to Free Frames
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COP 4600: Intro To OS (Memory Management – Part 2) Page 5 © Dr. Mark Llewellyn Assignment of Process Pages to Free Frames
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COP 4600: Intro To OS (Memory Management – Part 2) Page 6 © Dr. Mark Llewellyn Paging (cont.) Notice that process pages do not need to be loaded into contiguous page frames. (Recall our discussions of logical addressing.) With paging, a simple relocation register is no longer sufficient for calculating physical addresses at execution time. The OS maintains a page table for each process. The page table shows the frame location for each page of the process. Within the program, each logical address consists of a page number and an offset within the page. Recall that with simple partitioning, a logical address is the location of the word relative to the beginning of the program which the processor translated into a physical address. With paging, the logical-to-physical address translation is still done by processor hardware, but now the processor must know how to access the page table of the current process.
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COP 4600: Intro To OS (Memory Management – Part 2) Page 7 © Dr. Mark Llewellyn Paging (cont.) When presented with a logical address (page number, offset), the processor uses the page table to produce a physical address (page frame, offset). The next page, illustrates the page tables for the processes
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memory management - part 2 (8) - COP 4600 Summer 2011...

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