Lecture 02 - Memory Management, Early Systems

Lecture 02 - Memory Management, Early Systems - Chapter2...

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Chapter 2 Memory Management:  Early Systems
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After completing this chapter, you should be able to  describe: The basic functionality of the three memory  allocation schemes presented in this chapter: fixed  partitions, dynamic partitions, relocatable dynamic  partitions Best-fit memory allocation as well as first-fit  memory allocation schemes How a memory list keeps track of available  memory Understanding Operating Systems, Sixth Edition 2 2
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Understanding Operating Systems, Sixth Edition 3 The importance of deallocation of memory in a  dynamic partition system The importance of the bounds register in memory  allocation schemes The role of compaction and how it improves  memory allocation efficiency 3
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Management of main memory is critical. The performance of the entire   system has been  directly dependent on two things: How much memory is available How it is optimization while jobs are being processed. This chapter introduces: The memory manager (RAM) Core memory (primary storage)  Understanding Operating Systems, Sixth Edition 4 4
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This chapter introduces: Four types of memory allocation schemes Single-user systems Fixed partitions Dynamic partitions Relocatable dynamic partitions These early memory management schemes are seldom  used by today’s OSs but are important to study because  each one introduced fundamental concepts that helped  memory management evolve.    Understanding Operating Systems, Sixth Edition 5 5
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Commercially available in 1940s and 1950s Each program was loaded in its entirety into  memory and allocated as much contiguous memory  space allocated as it needed. If the program was too large and didn’t fit the  available memory space, it couldn’t be executed, Although early computers were physically large,  they had very little memory. Computers have only a finite amount of memory.  Understanding Operating Systems, Sixth Edition 6
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If a program doesn’t fit, then either the size of the  main memory must be increased or the program  must be modified. Making it smaller Using methods that allow program segments (partitions  made to the program) to be overlaid. Transfer segments of a program from secondary storage into  main memory for execution Two or more segments take turns occupying the same  memory locations. Understanding Operating Systems, Sixth Edition 7
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Program Segmentation   Slides Understanding Operating Systems, Sixth Edition 8
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The amount of work performed by the Memory  Manager is minimal. Only two hardware items are needed: 
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Lecture 02 - Memory Management, Early Systems - Chapter2...

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