Reference String in Operating System

When you go through topics like Page Replacement Algorithms you might have noticed that What is Reference String? In this article, we are going to discuss the topic Reference String in Operating Systems-Definition, Uses, Example with explanation, FAQs.

What is Reference String in OS?

Reference string is a concept that is used in memory management topics like page replacement algorithms. We can consider it as a sequence of numbers or sequence of strings .ie, a sequence of memory access requests while executing a program or any process. This request asks for a place in the program’s address space, which might have to access the data from the main memory.

NOTE

Here in the image (1) PAGE REFERENCE means REFERENCE STRING.

Consider a process P, which has memory access requests in a sequence of 1,3,0,3,5,6,3. This memory request sequence is called a Reference String.

1 comes first, if 1 is in the frame, page hit occurs. Else request the page from main memory and add it into frames. Then 3 comes, 0 comes, 3 comes, 5 comes, 6 comes, 3 comes as in the sequence of Reference String.

Types

• Sequential Reference String: Here strings follow a strict order like 1,2,3,4,5
• Random Reference String: Here the string will be in a non-predictable manner. That can be any random number like 1,6,3,9,5,1,...
• Looping Reference String: It follows a repetitive nature in the order of string elements like 1,2,3,1,2,3, …
• Localized Reference String: A localized reference string involves repeated requests for a specific memory location or a set of closely related memory locations like 5, 5, 5, 5, 5, 5.

Uses

• It helps to evaluate an algorithm. In the case of the Page replacement algorithm, there is FIFO, Optimal, and LRU; we can compare the page hits, and page faults of each algorithm very easily.
• It could help to make a more optimized page table for different processes.
• We can predict the need for data requirements in the future for a particular process by analyzing the trend of the Reference String sequence.

Advantages

• It helps to evaluate the efficiency of a page replacement algorithm.
• It helps to choose a better page replacement algorithm for a particular device or application.
• It helps to optimize memory and resource allocation.
• It could help the users to predict the future requirements of data.
• It could reveal the trend of memory requirement pattern.
• It helps to manage CPU cache memory.