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Memory management early_systems
1. Chapter 2 Memory Management: Early Systems Understanding Operating Systems, Fourth Edition
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4. Memory Management: Early Systems Understanding Operating Systems, Fourth Edition “ Memory is the primary and fundamental power, without which there could be no other intellectual operation.” —Samuel Johnson (1709–1784)
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9. Fixed Partitions (continued) Understanding Operating Systems, Fourth Edition Table 2.1: A simplified fixed partition memory table with the free partition shaded To allocate memory spaces to jobs, the operating system’s Memory Manager must keep a table as shown below:
10. Fixed Partitions (continued) Understanding Operating Systems, Fourth Edition Figure 2.1: Main memory use during fixed partition allocation of Table 2.1 NOTE: Job 3 must wait even though 70K of free space is available in Partition 1 where Job 1 occupies only 30K of the 100K available
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13. Dynamic Partitions (continued) Understanding Operating Systems, Fourth Edition Figure 2.2: Main memory use during dynamic partition allocation
14. Dynamic Partitions (continued) Understanding Operating Systems, Fourth Edition Figure 2.2 (continued): Main memory use during dynamic partition allocation
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17. Best-Fit Versus First-Fit Allocation (continued) Understanding Operating Systems, Fourth Edition Figure 2.3: An example of a first-fit free scheme
18. Best-Fit Versus First-Fit Allocation (continued) Understanding Operating Systems, Fourth Edition Figure 2.4: An example of a best-fit free scheme
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21. Best-Fit Versus First-Fit Allocation (continued) Understanding Operating Systems, Fourth Edition Table 2.2: Status of each memory block before and after a request is made for a block of 200 spaces using the first-fit algorithm
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23. Best-Fit Versus First-Fit Allocation (continued) Understanding Operating Systems, Fourth Edition Table 2.3: Status of each memory block before and after a request is made for a memory block of 200 spaces using the best -fit algorithm
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28. Case 1: Joining Two Free Blocks Understanding Operating Systems, Fourth Edition Table 2.4: Original free list before deallocation for Case 1
29. Case 1: Joining Two Free Blocks (continued) Understanding Operating Systems, Fourth Edition Table 2.5: Free list after deallocation for Case 1
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31. Case 2: Joining Three Free Blocks Understanding Operating Systems, Fourth Edition Table 2.6: Original free list before deallocation for Case 2
32. Case 2: Joining Three Free Blocks (continued) Understanding Operating Systems, Fourth Edition Table 2.7: Free list after job has released memory
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34. Case 3: Deallocating an Isolated Block Understanding Operating Systems, Fourth Edition Table 2.8: Original free list before deallocation for Case 3
35. Case 3: Deallocating an Isolated Block (continued) Understanding Operating Systems, Fourth Edition Table 2.9: The job to be deallocated is of size 445 and begins at location 8805. The asterisk indicates the soon-to - be-free memory block. Table 2.9: Memory list before deallocation
36. Case 3: Deallocating an Isolated Block (continued) Understanding Operating Systems, Fourth Edition Table 2.10: Busy list after the job has released its memory. The asterisk indicates the new null entry in the busy list.
37. Case 3: Deallocating an Isolated Block (continued) Understanding Operating Systems, Fourth Edition Table 2.11: Free list after the job has released its memory. The asterisk indicates the new free block entry replacing the null entry
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40. Relocatable Dynamic Partitions (continued) Understanding Operating Systems, Fourth Edition Figure 2.5: An assembly language program that performs a simple incremental operation
41. Relocatable Dynamic Partitions (continued) Understanding Operating Systems, Fourth Edition Figure 2.6: The original assembly language program after it has been processed by the assembler
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45. Relocatable Dynamic Partitions (continued) Understanding Operating Systems, Fourth Edition Figure 2.7: Three snapshots of memory before and after compaction
46. Relocatable Dynamic Partitions (continued) Understanding Operating Systems, Fourth Edition Figure 2.8: Contents of relocation register and close-up of Job 4 memory area (a) before relocation and (b) after relocation and compaction
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