8.2. Two Levels of MemoryA virtual view of memory storage, known as an address space, is presented to the application while the VM system transparently manages the virtual storage between RAM and secondary storage. Because RAM is significantly faster than disk (100 ns versus 10 ms, or approximately 100,000 times faster), the job of the VM system is to keep the most frequently referenced portions of memory in the faster primary storage. In the event of a RAM shortage, the VM system is required to free RAM by transferring infrequently used memory out to the backing store. By so doing, the VM system optimizes performance and removes the need for users to manage the allocation of their own memory requirements. |