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Virtual memory makes application programming easier by hiding fragmentation of physical memory; by delegating to the kernel the burden of managing the memory hierarchy (eliminating the need for the program to handle overlays explicitly); and, when each process is run in its own dedicated address space, by obviating the need to relocate program code or to access memory with relative addressing.
It is the smallest unit of data for memory management in an operating system that uses virtual memory. Similarly, a page frame is the smallest fixed-length contiguous block of physical memory into which memory pages are mapped by the operating system. [1] [2] [3]
A similar mechanism is used for memory-mapped files, which are mapped to virtual memory and loaded to physical memory on demand. When physical memory is not full this is a simple operation; the page is written back into physical memory, the page table and TLB are updated, and the instruction is restarted.
However, the page file only expands when it has been filled, which, in its default configuration, is 150% of the total amount of physical memory. [16] Thus the total demand for page file-backed virtual memory must exceed 250% of the computer's physical memory before the page file will expand.
Virtual addresses seen by the program are added to the contents of the base register to generate the physical address. The address is checked against the contents of the bounds register to prevent a process from accessing memory beyond its assigned segment. The operating system is not constrained by the hardware and can access all of physical ...
Memory virtualization technology follows from memory management architectures and virtual memory techniques. In both fields, the path of innovation has moved from tightly coupled relationships between logical and physical resources to more flexible, abstracted relationships where physical resources are allocated as needed.
An iconic example of virtual-to-physical address translation is virtual memory, where different pages of virtual address space map either to page file or to main memory physical address space. It is possible that several numerically different virtual addresses all refer to one physical address and hence to the same physical byte of RAM.
Through the process of paging, the contents of this virtual memory may move between physical memory and the page file, but it cannot exceed the sum of sizes of those two. As a percentage, commit charge is the utilization of this limit.