Virtual memory technique is used in modern OS which permits the execution of a program while it is partially available in memory thus providing an illusion of very large memory to the user and freeing the user from the concern of large program size. This uses a page replacement technique such as first in first out (FIFO), least recently used (LRU), optimal etc. to replace a page in memory when a frame is needed and no free frame is available in memory. Here page replacement policy severely affects the performance of virtual memory. It has been observed that LRU approximates optimal so LRU and its variants are quite common in use in operating system as a reasonable choice of page replacement algorithm. But LRU performs very poor by generating continuous page faults while accessing looping pattern if all the pages does not fit in the memory simultaneously. This paper presents a simple modified LRU algorithm called LRUL overcoming this problem using the concept of last use distance (LUD). It is observed that the new algorithm gives better results than LRU.

Operating system LRU page replacement algorithm.