Concept of locality of reference:
In computer science, locality of reference, also called the principle of locality, is the term applied
to situations where the same value or related storage locations are frequently accessed.
Suppose a programmers began writing programs using block structures. Following constructs are
block.
1. Compound statements
2. Loops
3. Functions
4. Files.
If a block is a loop consisting of N statements, and if the loop executes 100 times, then for next
100N instructions the control will remain within the loop.
The mechanism of keeping the program control confined to a block for maximum time is called
locality of reference. In this strategy, the program’s address space is divided into small blocks
and each blocks are stored in contiguous pages.
The advantage of this style of programming is that references become near and remain within a
small block on a page.
Thrashing:
The page fault frequency of a process depends upon whether the program was written using the
principle of locality of reference. If the programmer has not followed the principle, then very large
number of page faults occur, and the phenomenon is called Thrashing.
Causes of thrashing:
1. Unstructured program: In an unstructured program, the flow of control does not follow a well-
structured path. The address references of operands are made to distant location situation in page
s currently not available in working set of process. The ‘jump’ statements take a control all over,
within the various of the program. So the no of page faults increased.
