What is Virtual memory?
- Virtual memory is the separation of user logical memory from physical memory.
- This separation allows an extremely large virtual memory to be provided for programmers when only a smaller physical memory is available.
- Virtual memory is a technique that allows the execution of processes which are not completely available in memory.
- Following are the situations, when entire program is not required to be loaded fully in main memory.
- User written error handling routines are used only when an error occured in the data or computation.
- Certain options and features of a program may be used rarely.
- Many tables are assigned a fixed amount of address space even though only a small amount of the table is actually used.
- The ability to execute a program that is only partially in memory would counter many benefits.
- Less number of I/O would be needed to load or swap each user program into memory.
- A program would no longer be constrained by the amount of physical memory that is available.
- Each user program could take less physical memory, more programs could be run the same time, with a corresponding increase in CPU utilization and throughput.
- Virtual memory is commonly implemented by demand paging.
- It can also be implemented in a segmentation system.
- Demand segmentation can also be used to provide virtual memory.
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