What is Virtual Memory? What are the necessary layers of memory hierarchy that helps to create the virtual memory?


Virtual Memory is a memory management technique in which the computer user is given feeling that unlimited memory is available at his disposal for running programs. Here very large programs are run using small size physical memory. Large programs in secondary memory are divided into fixed size pages and available physical memory is divided into blocks. Block size and physical memory size is kept same. Few pages of program are loaded into the blocks and are executed. When new pages are required for execution they are loaded from secondary memory into one of the blocks replacing the earlier page stored in that block. Using this technique very large programs are executed using small size primary memories. To create virtual memory, two layers of memory is required. One is secondary memory to store large programs/data that is to be executed. Second layer is physical memory to store various pages that is needed currently for execention.

In segmented paged allocation, segmentation is used to facilitate sharing and protection. Paging is used to resolve the fragmentation and recomputing problems and demand paging eliminate the restriction on address space size. A segment table is used along with page tables. One page table is used for each segment and each segment have a corresponding segment page table entry. Using this segment table entry a page table is selected and various entries in that page table corresponds to various pages of that segment.

Post a Comment

0 Comments