Introduction to Computer Architecture
Virtual memory is a technique used by operating systems to provide the illusion of a larger amount of physical memory than is actually available. It does this by temporarily transferring pages of data from physical memory to disk storage, allowing the physical memory to be used for other purposes. Virtual memory systems also provide memory protection by isolating processes from each other and from the operating system itself.
Virtual memory management involves allocating and deallocating physical memory as needed, and managing the transfer of data between physical memory and disk storage. This process is handled by the operating system's memory manager, which keeps track of which pages of data are currently resident in physical memory and which have been temporarily moved to disk.
Paging is the most common virtual memory technique used by modern operating systems. In paging, the physical memory is divided into fixed-size pages, typically 4KB in size. Each page is mapped to a corresponding page in virtual memory, allowing the operating system to manage virtual memory in terms of fixed-size pages rather than in terms of the physical memory itself.
A page fault occurs when the operating system attempts to access a page of data that is not currently resident in physical memory. When this happens, the operating system must first allocate a page of physical memory to hold the data, and then transfer the data from disk storage to the newly-allocated page. Once the data is resident in physical memory, the operating system can access it as normal.
Virtual memory is a powerful technique used by modern operating systems to provide the illusion of a larger amount of physical memory than is actually available. By managing memory in terms of fixed-size pages, virtual memory systems are able to provide efficient and effective memory management, while also providing memory protection and isolation between processes.
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