virtual memory

Virtual memory - Chapter 10 Virtual Memory s Background s Demand Paging s Process Creation s Page Replacement s Allocation of Frames s Thrashing s

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Silberschatz, Galvin and Gagne 2002 10.1 Operating System Concepts Chapter 10: Virtual Memory Background Demand Paging Process Creation Page Replacement Allocation of Frames Thrashing Operating System Examples http://cne.gmu.edu/workbenches/vmsim/vmsim.html
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Silberschatz, Galvin and Gagne 2002 10.2 Operating System Concepts All memory management algorithms described till now have the same requirement that the process must be completely in system memory before it can execute. So they limit the maximal user program size to the size of the physical memory. In general, real user programs don't need to be completely in system memory while they execute
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Silberschatz, Galvin and Gagne 2002 10.3 Operating System Concepts example For example: programs often have code to handle unusual error events which very rarely occur in practice. This code is almost never executed. Even in those cases where the entire program is needed, it's not necessary for all parts of the program to be in memory at the same time. Executing a program that is partially in memory can have many benefits, not only for users but also for the system:
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Silberschatz, Galvin and Gagne 2002 10.4 Operating System Concepts A program is no longer limited by the size of physical memory that is available. Writing a program in a large virtual address space is more convenient. Because each user may take less physical memory, more user can be run at the same time. The CPU utilization and the system throughput may increase. Less I/O operation would be needed to load users into memory, so each user could run faster.
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Silberschatz, Galvin and Gagne 2002 10.5 Operating System Concepts Virtual memory management allows the execution of processes that are partially in system memory. So programming with very large virtual memory is possible. Virtual memory is implemented by demand paging , i.e., parts of user program expressed in pages are loaded into system memory if required. Demand segmentation can also be used to provide virtual memory. Because of the variable-sized feature of segments the associated segment replacement algorithms are more complex than page replacement algorithms. So we focus our attention on the demand paging algorithms.
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Silberschatz, Galvin and Gagne 2002 10.6 Operating System Concepts Demand paging Normally, user programs are kept in secondary memory, usually on a disk. When a program is to be executed, it is swapped into system memory in the following way: only those pages that will be used before the program will swapped out again are swapped in. Through this, swapping time and amount of physical memory needed can be decreased.
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Silberschatz, Galvin and Gagne 2002 10.7 Operating System Concepts Transfer of a Paged Memory to Contiguous Disk Space
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Silberschatz, Galvin and Gagne 2002 10.8 Operating System Concepts We will need some form of hardware support to
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This note was uploaded on 07/15/2011 for the course ECO 2023 taught by Professor Mr.raza during the Summer '10 term at FAU.

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Virtual memory - Chapter 10 Virtual Memory s Background s Demand Paging s Process Creation s Page Replacement s Allocation of Frames s Thrashing s

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