Virtual memory

Virtual memory - swapping is that the granularity was too...

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Virtual Memory
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Other Uses of Virtual Memory Another goal of VM is to speed up some of the tasks in the OS for example: Loading a program. The VM will load pages of the program as they are needed, instead of loading the program all at once. During fork the child gets a copy of the memory of the parent. However, parent and child will use the same memory as long as it is not modified, making the fork call faster. This is called “copy-on-write”. Shared Libraries across processes. Shared memory There are other examples that we will cover later.
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VM Implementations q Process Swapping: q The entire memory of the process is swapped in and out of memory q Segment Swapping q Entire parts of the program (process) are swapped in and out of memory (libraries, text, data, bss, etc. q Problems of process swapping and segment
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Unformatted text preview: swapping is that the granularity was too big and some pieces still in use could be swapped out together with the pieces that were not in use. Paging Virtual Memory Introduction • VM allows running processes that have memory requirements larger than available RAM to run in the computer. • f the following processes are running with the noted requirements: – IE (200MB), – MSWord (200MB), – Skype (70MB) – Operating System (1GB). • This would require 1.47GB of memory when there may only be 1GB of RAM available Virtual Memory Introduction • VM only keeps in RAM the memory that is currently in use. • The remaining memory is kept in disk in a special file called "swap space" • The VM idea was created by Peter Dening a former head of the CS Department at Purdue...
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