Index controllers are devices or software used to manage and organize data in databases or information systems. They help improve the speed and efficiency of data retrieval by creating an index, which is a structured list of data entries. This allows users to quickly locate specific information without having to search through all the data manually. In the context of search engines, index controllers play a crucial role in how information is stored and accessed. They ensure that relevant results are returned promptly when users enter queries, enhancing the overall user experience by making data more accessible and manageable.