Memory Management -2

Memory Management -2 - Operating Systems Fixed/Variable...

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Unformatted text preview: Operating Systems Fixed/Variable Partitioning 2 Real Memory Management • Background • Memory Management Requirements • Fixed/Static Partitioning • Variable/Dynamic Partitioning • Simple/Basic Paging • Simple/Basic Segmentation • Segmentation with Paging 3 Contiguous Allocation • An executing process must be loaded entirely in main memory (if overlays are not used). • Main memory is usually split into two (memory split) or more (memory division) partitions: – Resident operating system, usually held in low memory partition with interrupt vector. – User processes then held in high memory partitions. – Relocation-register scheme is used to protect user processes from each other, and from changing OS code and data. 4 Real Memory Management Techniques • Although the following simple/basic memory management techniques are not used in modern OSs, they lay the ground for a later proper discussion of virtual memory: – Fixed/Static Partitioning – Variable/Dynamic Partitioning – Simple/Basic Paging – Simple/Basic Segmentation 5 Fixed Partitioning • Partition main memory into a set of non- overlapping memory regions called partitions. • Fixed partitions can be of equal or unequal sizes. • Leftover space in partition, after program assignment, is called internal fragmentation. 6 Placement Algorithm with Partitions • Equal-size partitions: – If there is an available partition, a process can be loaded into that partition - • because all partitions are of equal size, it does not matter which partition is used. – If all partitions are occupied by blocked processes, choose one process to swap out to make room for the new process. 7 Placement Algorithm with Partitions • Unequal-size partitions, use of multiple queues: – assign each process to the smallest partition within which it will fit. – a queue exists for each partition size. – tries to minimize internal fragmentation....
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Memory Management -2 - Operating Systems Fixed/Variable...

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