unctionality.The logical address serves as a virtual address which is viewable by the user program. The Physical address, however, is not view able directly by the user program and the logical address is utilized as a resource to access the physical address with the aid of a pointer. MEMORY ALLOCATION METHODS The allocation methods define how the files are stored in the disk blocks. There are three main disk space or file allocation methods. 1. Contiguous Allocation 2. Linked Allocation 3. Indexed Allocation PAGING: A computer can address more memory than the amount physically installed on the system. This extra memory is actually called virtual memory and it is a section of a hard that's set up to emulate the computer's RAM. Paging technique plays an important role in implementing virtual memory.Paging is a memory management technique in which process address space is broken into blocks of the same size called pages (size is power of 2, between 512 bytes and 8192 bytes). The size of the process is measured in the number of pages.Similarly, main memory is divided into small fixed-sized blocks of (physical) memory called frames and the size of a frame is kept the same as that of a page to have optimum utilization of the main memory and to avoid external fragmentation. SEGMENTATION: Segmentation is a memory management technique in which each job is divided into several segments of different sizes, one for each module that contains pieces that perform related functions.Each segment is actually a different logical address space of the program. VIRTUAL MEMORY: A computer can address more memory than the amount physically installed on the system. This extra memory is actually called virtual memory and it is a section of a hard disk that's set up to emulate the computer's RAM. PAGE REPLACEMENT ALGORITHMS: In operating systems that use paging for memory management, page replacement algorithm are needed to decide which page needed to be replaced when new page comes in. Whenever a new page is referred and not present in memory, page fault occurs and Operating System replaces one of the existing pages with newly needed page. Different page replacement algorithms suggest different ways to decide which page to replace. The target for all algorithms is to reduce number of page faults. (i)First In First Out (FIFO) (ii)Optimal Page replacement (iii)Least Recently Used (iv)Page buffering algorithm (v)Least frequently Used (LFU) algorithm (vi)Most frequently Used (MFU) algorithm ALLOCATION OF FRAMES: An important aspect of operating systems, virtual memory is implemented using demand paging.Demand paging necessitates the development of a page-replacement algorithm and a frame allocation algorithm. Frame allocation algorithms are used if you have multiple processes; it helps decide how many frames to allocate to each process.