What Is External Searching in Data Structure?


Larry Thompson

External searching is a technique used in data structures to efficiently search for information stored outside the main memory. In this article, we will explore what external searching is, how it works, and its applications.

What is External Searching?

External searching, also known as external memory searching or disk-based searching, is a method of searching for data that exceeds the capacity of the available main memory. While internal searching algorithms are designed for data that can fit entirely in RAM, external searching algorithms are used when dealing with large datasets that need to be stored on secondary storage devices such as hard drives or solid-state drives (SSDs).

How does External Searching work?

In external searching, the data is divided into smaller blocks or pages and stored on secondary storage. The search algorithm reads these blocks from disk into main memory and performs the search operation. Since disk access is much slower than accessing data from RAM, external searching algorithms aim to minimize the number of disk I/O operations required to locate the desired information.

The Two Phases of External Searching:

  1. Search Phase:
  2. The search phase involves fetching relevant blocks from secondary storage into main memory and performing the search operation within these blocks. The most commonly used algorithm for this phase is the B-Tree algorithm.

  3. Move-To-Front Phase:
  4. In this phase, after finding the desired block during the search phase, it is moved to the front of the list of blocks in main memory. This optimization ensures that frequently accessed blocks remain in RAM for faster future searches.

Applications of External Searching

External searching plays a crucial role in various real-world applications where large datasets need to be searched efficiently. Some common applications include:

  • Database Systems: External searching is used in database systems to search for records, perform queries, and retrieve data from disk-based storage.
  • Web Search Engines: Search engines like Google use external searching techniques to index and retrieve web pages based on user queries.
  • File Systems: External searching algorithms are utilized in file systems to locate files stored on secondary storage devices.
  • Data Mining: Data mining algorithms often require efficient external searching to process large datasets and extract valuable patterns or information.


External searching is a powerful technique that allows us to search for information efficiently even when dealing with large datasets that cannot fit in main memory. By dividing data into smaller blocks and optimizing disk I/O operations, external searching algorithms enable faster access to information stored on secondary storage devices. Understanding external searching is essential for developers working with large-scale data processing applications.

So, next time you encounter the need to search through extensive datasets, remember the importance of external searching in making the process efficient!

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